I was watching some old Mario Batali cooking shows and he regularly used red onions in dishes that I thought were exclusive to yellow onion territory. I've always kept a distinction between red onions and yellow onions, never considering substituting one for the other. Reds are good pickled and raw in salads, but that's about all I've ever done with them. Yellows are the old standby, the standard for any mirepoix, sliced, chopped or minced as a garnish on a hamburger bun, fried rings and bake