Football just does weird things to people. I've mentioned my Man City supporting mate before. Outside football she's a rational, intelligent human being who does a very responsible and not unstressful job. She runs most of her life in a rational way and is quite "normal ".
But. She has nothing to do with red. Won't have a red car, furniture, paint, Christmas decorations, clothes, flowers (yes!), nothing.
I think it's a bit odd and taking things to extremes. My favourite colour is red (then purple!!), but I do have the odd blue possession and I had blue car once (didn't like it though!).