I've heard some guntubers and others say the green dot tends to get lost easier outdoors when shooting with a lot of grass/vegetation around whereas the red really stands out. I just personally prefer the red better but that's just personal preference...
For someone who's shot quite a bit near my cabin (me), I've found this to be true.
I do have one green dot, but I'll always buy red from now on. (all rifle dots)
The green woods makes the green dot disappear.