I am saying that his motives now are a moot point once he's shown he will vote based on skin color. There's simply no reason to give an admitted racist the benefit of the doubt on this issue, and yes your euphemism of "wanted to play a role in electing the first black president.." is actually "voted for him because he's black". Spin it how you like, Colin Powell basically showed and admitted that he voted for Obama because of the color of his skin (he endorsed, we don't know who he voted for though we have a good idea). Sure I understand his motives, but they are still racially motivated. Decisions based on color of skin instead of content of character are racist.
Powell chose the advancement of colored people over the advancement of the nation.