Is it off and on or constant? Does he rub or squint his eyes? Is there any discharge? If no to the questions and just red eyes then it probably wouldnt bother me. Riley often has red eyes for no reason. Perhaps your guy has some allergies. As long as they are completely normal in every other way and dont stay red all the time then i would be ok with that.
One of the things I was taught to look for while grooming was if the dog's eyes got red. It was one of the signs of stress we were supposed to be aware of to determine if continued grooming on a dog that was acting up was in the dogs best interest, or for that matter ours
I don't know why they would be doing it at home though, I would assume home isn't a stressful enviroment. The only time I see my personal dogs do it is when they reeeaaalllly don't want a bath, and are trying to get out of the tub.
Might be a question to ask your vet though, just in case