My guess as to why the request for red, is so they can easily spot the kids in their group in a crowd.

I read a cute story in a book by Joyce Maynard years ago, about taking her 3 small kids to a science museum, and dressing them in red (or some bright color) so she could keep track of them. But she found that lots of other parents had the same idea, and almost ALL the kids there were in bright colors. Then her youngest spilled or barfed or something, all over his shirt, so she just took the shirt off. Then he was really easy to spot, as he was the only kid running around with NO shirt at all!