In my experience with ACOGs in general, and this is just me, the red is useless indoors. You would think that the red would show up really well, but it doesn't. Red was the hardest to see, if I could see it at all. Outdoors, the red tends to bloom when it's really bright out forcing you to cover part of the fiber optic with tape to tame it.
I like the amber better than the red. It works very well indoors and out and it does well in situations where you are shooting from a place that is darker than where the target is, although this shooting condition lends itself to situations where the reticle takes on a shade that blends in to other color sometimes making the reticle hard to see. When it's really bright out, the reticle doesn't bloom like the red does. The amber really stands out most of the time.
I like the green the best. I works equally well indoors and out. When indoors, the green is really easy to see. When outdoors, it doesn't bloom. When shooting from a place that is darker than where the target is, seeing the reticle is no problem at all. I also haven't had any problems with losing the reticle in foliage. Yes, the reticle is green, but it's a different green, I guess.
I may have said this before, but I have a TA44S in amber and a TA33 in green. I'm getting ready to put my amber ACOG up for sale, once I source one in green.