Here's a few choices...you'll find it's a personal preference on what type and color. It really depends on what the use of the firearm will be...is it a concealed carry or a competition piece for example.
This is for a concealed carry weapon. My buddy has a Sig P239 with Trijicon Night sights on it and they seem to work well in the dark. They are all green. But i haven't seen any others so i wasn't sure if there were better. I have also heard of some being to bulky and snagging on the draw.