From a vision in multiple light conditions stand point, a green laser is going to far out do a red laser. Green is more visible in a wider awry of light conditions and is actually a "stronger" color for the human eye.
From a tactics standpoint I hate the idea of a laser on anything I own.
Lasers point two ways. They tell any OTHER individual exactly where you are and they tell anyone you light up the exact angle you have on them.
I would save your money and invest in some quality night sights personally.