No one can define race. There is no genetic difference between the races, and there is no point at which skin color or shape of face or body type can be legitimately broken in two. Color and facial shape and body type are all continuously changing from one person to the next.
On the census, people put themselves into whatever racial category they want to. This information is used to help distribute federal funds—with more going to disadvantaged areas. Congress seems to know what race is, since they pass laws saying who should get the money.
There are two racial attributes everyone has: the race they attribute to themselves and the race others attribute to them. If you go on looks alone, the two won’t agree very often.
What are the motivations for attributing a race to yourself or someone else? For some, it’s about status. You want to be a member of the dominant race because that gives you a leg up. Others can’t pass for the dominant race, so they may choose a race based on racial pride, or based on some other advantage it provides them, or based on cultural assimilation.
I don’t think white is a default position or generic position. White is the majority in the US, but it isn’t in Africa or Asia. I think people want to be white in the US if they can get away with it because it gives them an advantage. But that isn’t generic. White isn’t like white bread. White is a conglomeration of people with a lot of ethnic and cultural backgrounds, as is black or asian.
In one sense, they are all generic, since they all lump all kinds of people into one category. In another sense, they are distinct, since we all know the race we attribute to ourselves and we all know the race we attribute to others…. unless it isn’t clear, and then we ask them.
All races are generic. The concept of race is a bogus concept. No one really can give you a definition of what it is that works in all cases. So we lump people into a few generic categories. If white is generic, then so is every other race. However, white is not generic in the sense that people lump everyone into it if they can’t identify them as non-white.