The dimensions are a 1 to 1.9 ratio, same as the US flag. The colors have been sampled from Von Luschan's chromatic scale.
Some background on my thoughts as I threw this together:
I found that the most aesthetically pleasing arrangement of the colors was simply to put them in order of brightness. But this meant putting white on either the top or the bottom. If it was on the top, then it would imply that whites come first or are more important, and just the opposite for blacks. If it was on the bottom, then there would a suggestion of support for retributive inequality.
So I decided to put the darkest color in the middle, and place lighter colors on either side, alternating so as to keep the gradients as close together as possible. Whites are still on the bottom, but since asians are on top instead of blacks it seems less adversarial to me. Plus, blacks are in the middle, which, like being on top, emphasizes them, but is tempered by a reference to how racial equality's roots are in the struggle for black equality.
But then, I am a white, middle class, American male, who has been exposed primarily to the modern historical narrative of the Civil Rights Movement, and who has no expertise in matters of racial equality or relations. So I figure that just maybe for a design proposed by me to be something that everybody can get behind, regardless of race, ethnicity, or cultural origins, it needs to be exposed to a few diverse communities first, and get some revision to include the view points of other races before trying to take it to the mainstream.
As the creator, I release this design into the public domain, where it belongs.
Alternative proposals:
* Pribnow's deemphasis of skin colors and use of rotational symmetry