Why is the Atheist Movement so White?

There are certainly non-White atheists, including a couple of prominent atheist bloggers such as Friendly Atheist and the Infidel Guy, but the modern day atheist movement often seems very White to me. I am aware of the statistics showing that religiosity tends to be more common among African Americans than U.S. Whites, but I'm less clear about how other groups compare. I also wonder if such between-groups differences are large enough to explain the under-representation of racial and ethnic minorities in the atheist movement. If there are other relevant factors, what might they be? Any ideas?

This is mere speculation on my part, but I wonder if some persons of color view atheism as a less important part of their identity than do many White atheists. For example, I wonder if more White atheists may place "atheist" ahead of "White" in prioritizing the various components of their identity whereas some persons of color might do the opposite (e.g., placing "African American" ahead of "atheist"). I suppose another way to say this would be to suggest that atheism might be a more salient source of bigotry for Whites than for many persons of color.

Any other theories, or is my observation about the under-representation of minorities in the atheist movement simply wrong?