Flashy

from guizero import App,  PushButton

def blkwht():
    if button1.bg != 'white':
        button1.bg='white'
        button1.text_color='black'
    else:
        button1.bg='black'
        button1.text_color='white'

app = App("Flashing Button")

button1 = PushButton(app, text='Flashy')
button1.bg='white'
button1.repeat(1000, blkwht)