You do have a point, den, and you might be right. I cannot always tell Moslem Pakistanis apart from Indian Moslems, but I do think I can often distinguish Hindus from Sikhs and from Moslems by their mode of dress. Not all of them. Those who adopt European dress, I cannot tell apart at all, and some modes of dress are common to all religions, but here in Leicester, you see all sorts of clothing styles, and they do seem to relate to particular religions.
However, the dead Irish Catholics and Irish Protestants are not distinguished by race: they are all Irish. The sectarianism in Glasgow is not due to different races coming together, but different religions. The antagonists are from the same city!
Have you heard of Glasgow's Razor Gangs? There were such gangs in other British towns in the 30's, but in Glasgow, they were a particular problem. It was not just gang fights that were the trouble, but the fact that the gangs were divdied along religious/sectarian lines.