I'm strongly inclined to go with you on this one. I think we even talked about that, didn't we? Otoh, David can be "hip" when he needs to be, and is more informed about the music scene than Colby is, thus making him, by my estimation, more like Brown. Though since we don't know as much (canon) about Rafe and Brown as we do about Colby and David, we can certainly make things up. :-)

Skin color has absolutely nothing to do with it, most assuredly. But yeah, I'm thinking David & Rafe have the whole upstanding suit image going, whereas Colby & Brown are more easygoing.