L'argument background ne marche pas dans un Bouton TKinter

import string
from random import randint, choice
from tkinter import *


def generate_passwd():
    passwd_min = 6
    passwd_max = 18
    all_chars = string.ascii_letters + string.punctuation + string.digits
    password = "".join(choice(all_chars)for x in range(randint(passwd_min, passwd_max)))
    password_entry.delete(0, END)
    password_entry.insert(0, password)


window = Tk()
window.title("Générateur de mot de passe")
window.geometry()
window.minsize(720, 480)
window.iconbitmap('logo.png')
window.config(background='#5EFBDC')

frame = Frame(window, bg='#5EFBDC')

# ajouter image
width = 300
height = 300
image = PhotoImage(file="logo.png").zoom(50).subsample(60)
canvas = Canvas(frame, width=width, height=height, bg='#5EFBDC', bd=0, highlightthickness=0)
canvas.create_image(width/2, height/2, image=image)
canvas.grid(row=0, column=0, sticky=W)

right_frame = Frame(frame, bg='#5EFBDC')

label_title = Label(right_frame, text="Mot de passe", font=("Helvetica", 20), bg='#5EFBDC', fg='white')
label_title.pack()

# créer un champ/input
password_entry = Entry(right_frame, font=("Helvetica", 20), bg='#5EFBDC', fg='white')
password_entry.pack()

# créer un bouton
generate_button = Button(
    right_frame, text="Générer", font=("Arial", 20), bg='#68F004', fg='#68F004', relief=SUNKEN, bd=0, highlightthickness=0,
    command=generate_passwd
)   # curieusement l'argument 'bg=' n'a pas d'effet et le background reste gris alors qu'il devrait être vert.
generate_button.pack(pady=10, fill=X)

right_frame.grid(row=0, column=1, sticky=W)

frame.pack(expand=YES)

# créer barre de menu
menu_bar = Menu(window)

file_menu = Menu(menu_bar, tearoff=0)
file_menu.add_command(label="Nouveau", command=generate_passwd)
file_menu.add_command(label="Quitter", command=window.quit)
menu_bar.add_cascade(label="Fichier", menu=file_menu)

window.config(menu=menu_bar)

window.mainloop()