Maybe he just has a hard time recognizing white people? Generally speaking, people tend to have a harder time recognizing other people from different races, but maybe he's the opposite.
Probably not, but it's an idea.
I actually think someone brought this up on the last incarnation of the board. It does seem likely, doesn't it? I'd say there's a possibility, but Momma Barb never saw fit to take her child to the doctor for any reason other than state funds, so I don't think we'll ever know. It's impact on his life would also have been trivial in comparison to, say, him being an asshole to everyone he meets.
He recognized Snyder in a chance encounter when he wasn't expecting to see him, and he's probably only seen him a handful of times over the past few years. I suspect the biggest part of Chris's face-blindness is just that if he's not getting kicked out of a store by you or banging your B-cups, he doesn't care who the hell you are.