I usually pick a color I can see really well with against the enemy. In Dead Space (particularly 2), one of my biggest complaints is that the flashlight sometimes makes your aiming guides practically invisible, and I definitely aim by sight more so than "put center of screen here, please".
That was one of the reasons I liked Revelations, due to the laser color settings.
Gamertag is Madigari, for both Xbox 360 and PSN. Of all the things I've lost, I miss my originality the most.
I also agree with whoever wanted a rainbow laser sight as I would truly feel like a bad ass mofo while lighting fools up with deadly rainbow lazer with complementary rainbow bullets and rainbow weapon skins.
Stupidity isn't a virus, but it sure is spreading like one!