You could make a custom camo list similar to custom classes but separate and choose it before every round just like you would a custom class but you would choose both. That way you could have snow camo for snow maps, desert camo for desert maps, and black city camo for you get the idea!
Kind of a cool idea if it's restricted to selecting available options like gun camo or face paint in BO (although that's even more textures to keep track of in a game that already has frame rate issues on occasion). I'd prefer to allow for customization of the look of the character without fundamentally altering the ability to easily differentiate the team that each player is on.
If you want people to actually create their own patterns, then sorry, it's a stupid idea. The game is chatty enough as it is. Last thing I would want is to add to that just so some 14-year old can run around with a picture of a penis on his chest, because you KNOW that's what it'll end up being.