There are a myriad of factors that might influence that IQ score, and I haven't looked at the studies. Lack of wealth/opportunity I think is definitely a factor in the healthy development of the grey matter, as is access to good education.

Long/short, not sure. I'd be surprised if the colour of your skin objectively made a difference in IQ. Same with gender. Though, if the latter is true, I would probably use it with great exuberance on certain people I know e.g. my ex.