#Type "activebackground=" + your chosen background color between commas
col = Button(yourWindow, text='col', bg='gray25', activebackground='cyan')
# use activebackground and activeforeground properties to change the
# button color at the instance of being pressed.
btn = Button(frame, text="Click me", activebackground="blue",
activeforeground="white")
# activebackground will change the background of the button when clicked
# activeforeground will change the text color of the button when clicked