It would be fun to have that option. I'm guessing there are a lot of things above it on the priority list.
You probably know the usual colour of common team game opponents / friends. Helps provide identity and identification, like the colour of your car. I honestly think colour helps foster community to some degree. Why not bring that to ladder?
Mostly it's just fun. I'd have a hard time believing that this hasn't been suggested before, but search brought up nothing. I'm guessing this is one of those things that would be nice, but it'sn't critical.