Under Python 3.12 fill_color and back_color are ignored

[crystalfp]

I'm an happy user of qrcode that had to upgrade python to 3.12.
Now suddenly the colors I use are ignored. The following code generates an image with fill_color black and back_color white.

import qrcode
qr = qrcode.QRCode(version = None, box_size = 5)
qr.add_data('https://example.com/')
qr.make(fit=True)
img = qr.make_image(fill_color = 'white', back_color = 'black')
img.save('example.png')

Same behavior if I use the color tuples.
What should I do?
Thanks!
mario