It is very human if one is different then he becomes "black sheep", sometimes you notice that from the early ages once children in nursery, so that means it is in us from the very origin, this is our nature. The education of our children and explaining them why and what from early age will form the person his character, views and opinions.
I was always wondering if in animal world it is the same, like in your example with black and white sheep. When I was a child I loved white and did not black sheep, but of course nowadays because they are a bit rare I like black more. So the taste changes just depending on the circumstances and environment, I believe so.
I'd like to think that - it is just nature :)
natural, normal ..
I never had any preference over white or black sheep, I didn't have an orientation about colors so actually when I first saw a black sheep here, it just stood out but they all feel the same to me :)