Tableau bicolore triable

Bonjour,

Voici mon problème:
J'utilise un fichier sorttable.js (que j'ai trouvé sur le net) pour trier un tableau en cliquant sur l'entete de la colonne.
Ensuite, dans l'affichage de mon tableau , une colonne sur deux j'appelle une couleur pour le rendre bicolore.

Malheureusement, quand je le trie, les couleurs restent attachées aux colonnes et elles ne sont plus du tout alternées.

en gros ca donne ceci:
Avant triage:
Blanc
Bleu
Blanc
Bleu

Après triage
Bleu
Bleu
blanc
blanc

Voici mes fichiers:
Le tableau

<table class='sortable' border="1">
<?php
    $resultat = odbc_exec($odbc, "select num_site, nom_site, adr_site, cp_ville, ville_site, tel_site, mail_site from site order by nom_site;") or die (odbc_error());
	echo "
		<th class='donnees'>nom</th>
		<th class='donnees'>adresse</th>
		<th class='donnees'>cp</th>
		<th class='donnees'>ville</th>
		<th class='donnees'>telephone</th>
		<th class='donnees'>mail</th>
		<th class='donnees' colspan=3>choix</th>";
		$compt = odbc_exec($odbc,"select count(site.num_site) as comptedenum_site from site;");
		$compteur = odbc_result($compt,1);
			for ($i=1;$i<=$compteur;$i++)
			{
				$donnees = odbc_fetch_array($resultat,$i);
					if ($i%2 == 0)
					{
					echo '<form method="post" action="gestion/site_mod.php">
					<input type="hidden" name="num_site" value="' . $donnees['num_site'] . '" />';
			        echo "<tr><td value='nom_site'>";
			        echo $donnees['nom_site'];
			        echo "</td>";
					echo "<td value='adr_site'>";
			        echo $donnees['adr_site'];
			        echo "</td>";
					echo "<td value='cp_ville'>";
					echo $donnees['cp_ville'];
					echo "</td>";
					echo "<td value='ville_site'>";
					echo $donnees['Ville_site'];
					echo "</td>";
					echo "<td value='tel_site'>";
			        echo $donnees['tel_site'];
			        echo "</td>";
					echo "<td value='mail_site'>";
					echo "<a href=mailto:".$donnees['mail_site'].">".$donnees['mail_site']."</a>";
					echo "</td>";
					echo "<td class='donnees'>";?>
					<a href='gestion/site_visu.php?Num_site=<?php echo $donnees['Num_site']; ?>'<img src='style/image/eye.png'></a> <?php
					echo "</td>";
					echo "<td class='donnees'>";
					echo '<a href="'. $value['Modifier'].'" onclick="window.open(\'gestion/site_mod.php?Num_site='.$donnees['Num_site'].'\',\'\',\'toolbar=no,status=no,width=500,height=380,scrollbars=no,location=no,resize=no,menubar=no\');return false" title="Modifier"><img src="style/image/kedit.png"></a> ';
					echo "</td>";
					echo "<td class='donnees'>";?>
					<a href="gestion/site_suppr.php?Num_site=<?php echo $donnees['Num_site']; ?>" onclick="return(confirm('Etes-vous sûr de vouloir supprimer cette entrée?'));"><img src="style/image/cross.png" title="Supprimer"></a>
					<?php
					echo "</td></tr>";
					echo '</form>';
				}
				else
				{
					echo "<tr><td style='background-color:#f0f0f9' value='nom_site'>";
			        echo $donnees['Nom_site'];
			        echo "</td>";
					echo "<td style='background-color:#f0f0f9' value='adr_site'>";
			        echo $donnees['adr_site'];
			        echo "</td>";
					echo "<td style='background-color:#f0f0f9' value='cp_ville'>";
					echo $donnees['CP_ville'];
					echo "</td>";
					echo "<td style='background-color:#f0f0f9' value='ville_site'>";
					echo $donnees['Ville_site'];
					echo "</td>";
					echo "<td style='background-color:#f0f0f9' value='tel_site'>";
			        echo $donnees['tel_site'];
			        echo "</td>";
					echo "<td style='background-color:#f0f0f9' value='mail_site'>";
					echo "<a href=mailto:".$donnees['mail_site'].">".$donnees['mail_site']."</a>";
					echo "</td>";
					echo "<td style='background-color:#f0f0f9' class='donnees'>";?>
					<a href='gestion/site_visu.php?Num_site=<?php echo $donnees['Num_site']; ?>'<img src='style/image/eye.png'></a> <?php
					echo "</td>";
					echo "<td style='background-color:#f0f0f9' class='donnees'>";
					echo '<a href="'. $value['Modifier'].'" onclick="window.open(\'gestion/site_mod.php?Num_site='.$donnees['Num_site'].'\',\'\',\'toolbar=no,status=no,width=500,height=380,scrollbars=no,location=no,resize=no,menubar=no\');return false" title="Modifier"><img src="style/image/kedit.png"></a> ';
					echo "</td>";
					echo "<td style='background-color:#f0f0f9' class='donnees'>";?>
					<a href="gestion/site_suppr.php?Num_site=<?php echo $donnees['Num_site']; ?>" onclick="return(confirm('Etes-vous sûr de vouloir supprimer cette entrée?'));"><img src="style/image/cross.png" title="Supprimer"></a>
					<?php
					echo "</td></tr>";
					echo '</form>';
				}
			}
 ?>
</table>

Le script javascript:

var stIsIE = /*@cc_on!@*/false;

sorttable = {
  init: function() {
    // quit if this function has already been called
    if (arguments.callee.done) return;
    // flag this function so we don't do the same thing twice
    arguments.callee.done = true;
    // kill the timer
    if (_timer) clearInterval(_timer);
    
    if (!document.createElement || !document.getElementsByTagName) return;
    
    sorttable.DATE_RE = /^(\d\d?)[\/\.-](\d\d?)[\/\.-]((\d\d)?\d\d)$/;
    
    forEach(document.getElementsByTagName('table'), function(table) {
      if (table.className.search(/\bsortable\b/) != -1) {
        sorttable.makeSortable(table);
      }
    });
    
  },
  
  makeSortable: function(table) {
    if (table.getElementsByTagName('thead').length == 0) {
      // table doesn't have a tHead. Since it should have, create one and
      // put the first table row in it.
      the = document.createElement('thead');
      the.appendChild(table.rows[0]);
      table.insertBefore(the,table.firstChild);
    }
    // Safari doesn't support table.tHead, sigh
    if (table.tHead == null) table.tHead = table.getElementsByTagName('thead')[0];
    
    if (table.tHead.rows.length != 1) return; // can't cope with two header rows
    
    // Sorttable v1 put rows with a class of "sortbottom" at the bottom (as
    // "total" rows, for example). This is B&R, since what you're supposed
    // to do is put them in a tfoot. So, if there are sortbottom rows,
    // for backwards compatibility, move them to tfoot (creating it if needed).
    sortbottomrows = [];
    for (var i=0; i<table.rows.length; i++) {
      if (table.rows[i].className.search(/\bsortbottom\b/) != -1) {
        sortbottomrows[sortbottomrows.length] = table.rows[i];
      }
    }
    if (sortbottomrows) {
      if (table.tFoot == null) {
        // table doesn't have a tfoot. Create one.
        tfo = document.createElement('tfoot');
        table.appendChild(tfo);
      }
      for (var i=0; i<sortbottomrows.length; i++) {
        tfo.appendChild(sortbottomrows[i]);
      }
      delete sortbottomrows;
    }
    
    // work through each column and calculate its type
    headrow = table.tHead.rows[0].cells;
    for (var i=0; i<headrow.length; i++) {
      // manually override the type with a sorttable_type attribute
      if (!headrow[i].className.match(/\bsorttable_nosort\b/)) { // skip this col
        mtch = headrow[i].className.match(/\bsorttable_([a-z0-9]+)\b/);
        if (mtch) { override = mtch[1]; }
	      if (mtch && typeof sorttable["sort_"+override] == 'function') {
	        headrow[i].sorttable_sortfunction = sorttable["sort_"+override];
	      } else {
	        headrow[i].sorttable_sortfunction = sorttable.guessType(table,i);
	      }
	      // make it clickable to sort
	      headrow[i].sorttable_columnindex = i;
	      headrow[i].sorttable_tbody = table.tBodies[0];
	      dean_addEvent(headrow[i],"click", function(e) {

          if (this.className.search(/\bsorttable_sorted\b/) != -1) {
            // if we're already sorted by this column, just 
            // reverse the table, which is quicker
            sorttable.reverse(this.sorttable_tbody);
            this.className = this.className.replace('sorttable_sorted',
                                                    'sorttable_sorted_reverse');
            this.removeChild(document.getElementById('sorttable_sortfwdind'));
            sortrevind = document.createElement('span');
            sortrevind.id = "sorttable_sortrevind";
            sortrevind.innerHTML = stIsIE ? '&nbsp<font face="webdings">5</font>' : '&nbsp;&#x25B4;';
            this.appendChild(sortrevind);
            return;
          }
          if (this.className.search(/\bsorttable_sorted_reverse\b/) != -1) {
            // if we're already sorted by this column in reverse, just 
            // re-reverse the table, which is quicker
            sorttable.reverse(this.sorttable_tbody);
            this.className = this.className.replace('sorttable_sorted_reverse',
                                                    'sorttable_sorted');
            this.removeChild(document.getElementById('sorttable_sortrevind'));
            sortfwdind = document.createElement('span');
            sortfwdind.id = "sorttable_sortfwdind";
            sortfwdind.innerHTML = stIsIE ? '&nbsp<font face="webdings">6</font>' : '&nbsp;&#x25BE;';
            this.appendChild(sortfwdind);
            return;
          }
          
          // remove sorttable_sorted classes
          theadrow = this.parentNode;
          forEach(theadrow.childNodes, function(cell) {
            if (cell.nodeType == 1) { // an element
              cell.className = cell.className.replace('sorttable_sorted_reverse','');
              cell.className = cell.className.replace('sorttable_sorted','');
            }
          });
          sortfwdind = document.getElementById('sorttable_sortfwdind');
          if (sortfwdind) { sortfwdind.parentNode.removeChild(sortfwdind); }
          sortrevind = document.getElementById('sorttable_sortrevind');
          if (sortrevind) { sortrevind.parentNode.removeChild(sortrevind); }
          
          this.className += ' sorttable_sorted';
          sortfwdind = document.createElement('span');
          sortfwdind.id = "sorttable_sortfwdind";
          sortfwdind.innerHTML = stIsIE ? '&nbsp<font face="webdings">6</font>' : '&nbsp;&#x25BE;';
          this.appendChild(sortfwdind);

	        // build an array to sort. This is a Schwartzian transform thing,
	        // i.e., we "decorate" each row with the actual sort key,
	        // sort based on the sort keys, and then put the rows back in order
	        // which is a lot faster because you only do getInnerText once per row
	        row_array = [];
	        col = this.sorttable_columnindex;
	        rows = this.sorttable_tbody.rows;
	        for (var j=0; j<rows.length; j++) {
	          row_array[row_array.length] = [sorttable.getInnerText(rows[j].cells[col]), rows[j]];
	        }
	        /* If you want a stable sort, uncomment the following line */
	        //sorttable.shaker_sort(row_array, this.sorttable_sortfunction);
	        /* and comment out this one */
	        row_array.sort(this.sorttable_sortfunction);
	        
	        tb = this.sorttable_tbody;
	        for (var j=0; j<row_array.length; j++) {
	          tb.appendChild(row_array[j][1]);
	        }
	        
	        delete row_array;
	      });
	    }
    }
  },
  
  guessType: function(table, column) {
    // guess the type of a column based on its first non-blank row
    sortfn = sorttable.sort_alpha;
    for (var i=0; i<table.tBodies[0].rows.length; i++) {
      text = sorttable.getInnerText(table.tBodies[0].rows[i].cells[column]);
      if (text != '') {
        if (text.match(/^-?[?$?]?[\d,.]+%?$/)) {
          return sorttable.sort_numeric;
        }
        // check for a date: dd/mm/yyyy or dd/mm/yy 
        // can have / or . or - as separator
        // can be mm/dd as well
        possdate = text.match(sorttable.DATE_RE)
        if (possdate) {
          // looks like a date
          first = parseInt(possdate[1]);
          second = parseInt(possdate[2]);
          if (first > 12) {
            // definitely dd/mm
            return sorttable.sort_ddmm;
          } else if (second > 12) {
            return sorttable.sort_mmdd;
          } else {
            // looks like a date, but we can't tell which, so assume
            // that it's dd/mm (English imperialism!) and keep looking
            sortfn = sorttable.sort_ddmm;
          }
        }
      }
    }
    return sortfn;
  },
  
  getInnerText: function(node) {
    // gets the text we want to use for sorting for a cell.
    // strips leading and trailing whitespace.
    // this is *not* a generic getInnerText function; it's special to sorttable.
    // for example, you can override the cell text with a customkey attribute.
    // it also gets .value for <input> fields.
    
    hasInputs = (typeof node.getElementsByTagName == 'function') &&
                 node.getElementsByTagName('input').length;
    
    if (node.getAttribute("sorttable_customkey") != null) {
      return node.getAttribute("sorttable_customkey");
    }
    else if (typeof node.textContent != 'undefined' && !hasInputs) {
      return node.textContent.replace(/^\s+|\s+$/g, '');
    }
    else if (typeof node.innerText != 'undefined' && !hasInputs) {
      return node.innerText.replace(/^\s+|\s+$/g, '');
    }
    else if (typeof node.text != 'undefined' && !hasInputs) {
      return node.text.replace(/^\s+|\s+$/g, '');
    }
    else {
      switch (node.nodeType) {
        case 3:
          if (node.nodeName.toLowerCase() == 'input') {
            return node.value.replace(/^\s+|\s+$/g, '');
          }
        case 4:
          return node.nodeValue.replace(/^\s+|\s+$/g, '');
          break;
        case 1:
        case 11:
          var innerText = '';
          for (var i = 0; i < node.childNodes.length; i++) {
            innerText += sorttable.getInnerText(node.childNodes[i]);
          }
          return innerText.replace(/^\s+|\s+$/g, '');
          break;
        default:
          return '';
      }
    }
  },
  
  reverse: function(tbody) {
    // reverse the rows in a tbody
    newrows = [];
    for (var i=0; i<tbody.rows.length; i++) {
      newrows[newrows.length] = tbody.rows[i];
    }
    for (var i=newrows.length-1; i>=0; i--) {
       tbody.appendChild(newrows[i]);
    }
    delete newrows;
  },
  
  /* sort functions
     each sort function takes two parameters, a and b
     you are comparing a[0] and b[0] */
  sort_numeric: function(a,b) {
    aa = parseFloat(a[0].replace(/[^0-9.-]/g,''));
    if (isNaN(aa)) aa = 0;
    bb = parseFloat(b[0].replace(/[^0-9.-]/g,'')); 
    if (isNaN(bb)) bb = 0;
    return aa-bb;
  },
  sort_alpha: function(a,b) {
    if (a[0]==b[0]) return 0;
    if (a[0]<b[0]) return -1;
    return 1;
  },
  sort_ddmm: function(a,b) {
    mtch = a[0].match(sorttable.DATE_RE);
    y = mtch[3]; m = mtch[2]; d = mtch[1];
    if (m.length == 1) m = '0'+m;
    if (d.length == 1) d = '0'+d;
    dt1 = y+m+d;
    mtch = b[0].match(sorttable.DATE_RE);
    y = mtch[3]; m = mtch[2]; d = mtch[1];
    if (m.length == 1) m = '0'+m;
    if (d.length == 1) d = '0'+d;
    dt2 = y+m+d;
    if (dt1==dt2) return 0;
    if (dt1<dt2) return -1;
    return 1;
  },
  sort_mmdd: function(a,b) {
    mtch = a[0].match(sorttable.DATE_RE);
    y = mtch[3]; d = mtch[2]; m = mtch[1];
    if (m.length == 1) m = '0'+m;
    if (d.length == 1) d = '0'+d;
    dt1 = y+m+d;
    mtch = b[0].match(sorttable.DATE_RE);
    y = mtch[3]; d = mtch[2]; m = mtch[1];
    if (m.length == 1) m = '0'+m;
    if (d.length == 1) d = '0'+d;
    dt2 = y+m+d;
    if (dt1==dt2) return 0;
    if (dt1<dt2) return -1;
    return 1;
  },
  
  shaker_sort: function(list, comp_func) {
    // A stable sort function to allow multi-level sorting of data
    // see: https://en.wikipedia.org/wiki/Cocktail_sort
    // thanks to Joseph Nahmias
    var b = 0;
    var t = list.length - 1;
    var swap = true;

    while(swap) {
        swap = false;
        for(var i = b; i < t; ++i) {
            if ( comp_func(list[i], list[i+1]) > 0 ) {
                var q = list[i]; list[i] = list[i+1]; list[i+1] = q;
                swap = true;
            }
        } // for
        t--;

        if (!swap) break;

        for(var i = t; i > b; --i) {
            if ( comp_func(list[i], list[i-1]) < 0 ) {
                var q = list[i]; list[i] = list[i-1]; list[i-1] = q;
                swap = true;
            }
        } // for
        b++;

    } // while(swap)
  }  
}

/* ******************************************************************
   Supporting functions: bundled here to avoid depending on a library
   ****************************************************************** */

// Dean Edwards/Matthias Miller/John Resig

/* for Mozilla/Opera9 */
if (document.addEventListener) {
    document.addEventListener("DOMContentLoaded", sorttable.init, false);
}

/* for Internet Explorer */
/*@cc_on @*/
/*@if (@_win32)
    document.write("<script id=__ie_onload defer src=javascript:void(0)><\/script>");
    var script = document.getElementById("__ie_onload");
    script.onreadystatechange = function() {
        if (this.readyState == "complete") {
            sorttable.init(); // call the onload handler
        }
    };
/*@end @*/

/* for Safari */
if (/WebKit/i.test(navigator.userAgent)) { // sniff
    var _timer = setInterval(function() {
        if (/loaded|complete/.test(document.readyState)) {
            sorttable.init(); // call the onload handler
        }
    }, 10);
}

/* for other browsers */
window.onload = sorttable.init;

// written by Dean Edwards, 2005
// with input from Tino Zijdel, Matthias Miller, Diego Perini

// http://dean.edwards.name/weblog/2005/10/add-event/

function dean_addEvent(element, type, handler) {
	if (element.addEventListener) {
		element.addEventListener(type, handler, false);
	} else {
		// assign each event handler a unique ID
		if (!handler.$$guid) handler.$$guid = dean_addEvent.guid++;
		// create a hash table of event types for the element
		if (!element.events) element.events = {};
		// create a hash table of event handlers for each element/event pair
		var handlers = element.events[type];
		if (!handlers) {
			handlers = element.events[type] = {};
			// store the existing event handler (if there is one)
			if (element["on" + type]) {
				handlers[0] = element["on" + type];
			}
		}
		// store the event handler in the hash table
		handlers[handler.$$guid] = handler;
		// assign a global event handler to do all the work
		element["on" + type] = handleEvent;
	}
};
// a counter used to create unique IDs
dean_addEvent.guid = 1;

function removeEvent(element, type, handler) {
	if (element.removeEventListener) {
		element.removeEventListener(type, handler, false);
	} else {
		// delete the event handler from the hash table
		if (element.events && element.events[type]) {
			delete element.events[type][handler.$$guid];
		}
	}
};

function handleEvent(event) {
	var returnValue = true;
	// grab the event object (IE uses a global event object)
	event = event || fixEvent(((this.ownerDocument || this.document || this).parentWindow || window).event);
	// get a reference to the hash table of event handlers
	var handlers = this.events[event.type];
	// execute each event handler
	for (var i in handlers) {
		this.$$handleEvent = handlers[i];
		if (this.$$handleEvent(event) === false) {
			returnValue = false;
		}
	}
	return returnValue;
};

function fixEvent(event) {
	// add W3C standard event methods
	event.preventDefault = fixEvent.preventDefault;
	event.stopPropagation = fixEvent.stopPropagation;
	return event;
};
fixEvent.preventDefault = function() {
	this.returnValue = false;
};
fixEvent.stopPropagation = function() {
  this.cancelBubble = true;
}

// Dean's forEach: http://dean.edwards.name/base/forEach.js
/*
	forEach, version 1.0
	Copyright 2006, Dean Edwards
	License: https://opensource.org/licenses/mit-license.php
*/

// array-like enumeration
if (!Array.forEach) { // mozilla already supports this
	Array.forEach = function(array, block, context) {
		for (var i = 0; i < array.length; i++) {
			block.call(context, array[i], i, array);
		}
	};
}

// generic enumeration
Function.prototype.forEach = function(object, block, context) {
	for (var key in object) {
		if (typeof this.prototype[key] == "undefined") {
			block.call(context, object[key], key, object);
		}
	}
};

// character enumeration
String.forEach = function(string, block, context) {
	Array.forEach(string.split(""), function(chr, index) {
		block.call(context, chr, index, string);
	});
};

// globally resolve forEach enumeration
var forEach = function(object, block, context) {
	if (object) {
		var resolve = Object; // default
		if (object instanceof Function) {
			// functions have a "length" property
			resolve = Function;
		} else if (object.forEach instanceof Function) {
			// the object implements a custom forEach method so use that
			object.forEach(block, context);
			return;
		} else if (typeof object == "string") {
			// the object is a string
			resolve = String;
		} else if (typeof object.length == "number") {
			// the object is array-like
			resolve = Array;
		}
		resolve.forEach(object, block, context);
	}
};

Merci de votre aide car je ne comprend vraiment rien au javascript.