I love my 5DIII, but yeah--the AF points can be hard to see in low light. I've been doing quite a bit of stuff at night recently, and I wish they could work out a solution like they did for the 1DX. In most cases it isn't too much of an issue. but in situations where you are moving the AF points around it can make life a little more challenging. Doesn't dent my enthusiasm for the camera; and I guess the fact that I can shoot in situations where it is dark enough to make this an issue shows how well it does at high ISOs. So...
Wish the AF points had a red / blinky / low light "option," but not crying about it anyway. (HOWEVER--I suspect someone shooting very "active" situations in the dark might find this to be a more serious concern... I remember another thread a while back in which some guy was shooting dancers in a dark theater. For his purpose, the dark AF points might be more of a concern).