Would the CZ 16-80 be an upgrade from 17-50 2.8 if keeping both?

I see some brightness differences, but I wouldn't equate that with "color" differences. Very small adjustments in EV would seem to bring all three lenses into comparable range. At least, based on what you've posted, I'd be hesitant to jump to the CZ as "better" because of color. (Apart from the tonal differences, I can't find much to distinguish between the three.)