One of the factors people don't realize is that their perceptions are shaped by what they are told. In North America, and most of the world due to colonialism, there is a strong influence through the media to only promote white people as the prettiest. When you are young, you want to be with the best. The "best" is what you and your friends believe it to be. This consensus is shaped in part by what media owners tell young people who the best is. The obvious examples are like this:
http://www.youtube.com/watch?v=_RUiKkPqXjY&feature=related
http://www.youtube.com/watch?v=EZ6T5waiiOI&feature=related
http://www.youtube.com/watch?v=uIQZAQLeJmg
None of these people are particularly attractive, all that talented, but promoters tell young people this is who you will like, and they do. Early formation of these impressions shape what you perceive throughout your life, that's why media owners know how powerful a commodity media ownership is. You get to control the way people think, and all the while those same people will not even be aware that this type of social progamming is going on.
Now if the programming is racist (as it is in Canada, and most of the Western world) then you inevitably will also shape these racist perceptions in each and every young generation, and this perception will last a lifetime. You change that representation to Indian. Black, and Chinese, and be assured that social perceptions will change to perceive those groups as the most desirable. It's as simple as that. The reason white people in western societies are promoted in this way, is that they are the majority consumer, and in order to sell a product or a lifestyle (as shows and movies do), producers of products need to find people to sell their product whom the general masses identify with and aspire to be. In Western Markets, it's the white person. In the rest of the world, it's the white person (largely due to colonialism). Only in societies that have been able to maintain their cultural identity apart from the West (and I'm not talking about Hong Kong or India), will you see more representations of persons of color that dominate, and the society follows. It's hard to believe, but there are societies out there that don't see white people as the top of the food chain, and those places the society seems to be less racist.
Western societies are dominated by racist, "christian" white people. In this type of society, they are marketed as the top of the food chain. But that doesn't necessarily make it so. However, living in this type of environment, it is easy to see why there is a strong preference for this group, even by people of color. All these things influence the way we perceive one another, and are strong influences. They shape our identities and of those around us. Peer pressure causes anyone who is capable of independently thinking to conform, or they risk social isolation.
So someone who lives in this society and says "I'm not racist" I just prefer X person to Y, doesn't have a clear grasp of the dynamics that are going on that are imposed upon us to shape our perceptions of the people around us. This is a racist country, full of racist people, who all believe they are not racist.