Not irrelevant ones, though - I suspect many of us have been musing along the same lines.
Anecdote time:
A few years ago, my sister went to pick up my nephew from kindergarten. He was around 3 at the time. She asked him what he'd done that day, who he had played with, and so forth. Well, he'd mostly played with X - he said. My sister, not being entirely sure who X was, asked: "Who's X, then - is that the Black kid?" There was only one Black (male) kid in my nephew's age group in that particular kindergarten at the time. My nephew didn't quite understand what she meant, but after a moment's hesitation he said: "He's got a yellow jacket."
Now he's six. And now he refers to certain of his school mates as being "brown" (as opposed to himself, who is not "brown"). I recently asked him - after hearing him refer to X as "brown" - what he, himself was: "So, he's brown - what are you then, are you white?" He denied this - because "white" is the colour of, say, snow or a sheet of paper. He wasn't sure what to call the colour of his own skin, but it definitely wasn't "white".
