You raise an interesting point about racism and skin colour. I believe racism is more likely to be based around culture than physical appearance or skin colour. Different cultures do things differently and have different practices and understanding about what is consider acceptable or unacceptable behaviour. It is quite easy for people to associate people of a particular race with a particular culture. It would be nice to collect reliable data on why people are racist. Unfortunately, the topic is taboo to even the most racist people that I doubt we could get honest responses.