When we lived in the mountains, I had a friend over to play. (Probably just an acquaintance.) We played with a set of semi-trucks I had. When he linked a red truck to a gray trailer, I asked him - in a loud and mean way that I never would have expected of myself - "Don't you know your colors??" As if the only way to play trucks was the way I had always done it, with the colors of the trucks matching their trailers.