In the Stack Exchange Data Explorer, the icon color for the various sites *seems** incorrect: Whenever I select a main site, the icon is greyed out, and when ever I select the corresponding meta site, the icon is colored.
My initial instinct was to think that the colors of the main/meta sites following the "Switch sites:" prompt should be switched. (Actually, it seems like it's just a UI thing. See the edit below.)
*Edit: Actually, the colors are technically not incorrect, since (as Jeremy Banks has pointed out) the icon shows "the other" site of the main/meta pair, and clicking on it is for switching to the respective other site. See the comment thread for some UI improvement ideas.