First, greetings fellow old fart!
1. You will find fiber optic sights can be very helpful.
2. Color. I prefer green myself. I find it just a little bright for the same size. Having said that, the fiber is dirt cheap.
Try both. You can also go to a hobby store and find colored rods which might give you an option before you buy new ones.
2. Dimensions. Thats for your specific piece. If you look at the Dawson sight and go to CZ, when you click it there will be a long list of widths and heights.
Heights are more important for your rear sight. This is helpful:
https://dawsonprecision.com/sight-calculator/
Width: the wider the better for shorter distance or tactical shooting. You'll note M&P pro's fiber optic sight is almost fat. Per Dawson: Most action shooters go with a .100" to .105" wide front sight.
So if you go fatter you'll see it better (or more precisely acquire it better) but because its fatter its not as accurate at distance ( aka 25 yards).
I'd personally lean towards the .105 or even .110 if your particular sight has that option.
Hopefully others will opine as well especially with more sources. Dawson used to have a nice link discussing thickness as well but I can't find it.
One other note: replacing fibers in your sight is really really easy. If I were less lazy I'd probably replace the fiber every three months or so. News ones to me are brighter. It takes 5 minutes MAX and requires just a lighter and a simple nail clipper.
