I'm thinking/hoping he's kinda making that point. If you take 15/16 white paint and 1/16th black you'd end up with light-grey paint. Not with white, not with black. Yet people focus so much on race that they can't call themselves or others American or even simply human, it has to be 'White', 'Black', 'Asian', etc. Most 'blacks' in Africa are mixed too, and most 'whites' and 'asians' around the world are a mix of different 'races' as well. There's a reason why there are so many similarities between for example Arabs, Indians and the Latin American population. They're all mixes.
The vast majority of 'whites' in the US are mixes themselves from different European and Asian people:
http://en.wikipedia.org/wiki/Migration_Period
I like many 'types' of girls'. I'm not too fond of very dark skin, but also not of 'extremely white'. I like a large range between that though. It differs per person, but in many cases sticking with a certain 'race' depends on both group culture and availability. Among religious groups there is often huge pressure (more on the women than on the men) to marry within the religious group. Stereotypical prejudices can accomplish the same, where the parents or the rest of the community pushes people into believing that certain 'races' are bad and that you should not mix to 'keep your race pure'. And that is done by people from all races.