Asymmetrical Information

So here's a serious offhand

So here's a serious offhand question: why the hell do women in Saudi Arabia and like countries cover themselves head to toe in black?

No, that was not an invitation for comments about the Islamic interpretation of the Koranic verses regarding the attire of women (which do not, by the way, mention anything about dressing up like a bed every time you leave the house). What I want to know is, why black? In the world's hottest, sunniest, most miserably prickly-heat-inducing climate, why are these women wrapping themselves in fabric that absorbs heat rather than reflecting it? I mean, maybe the images I'm seeing on television are not a representative sample, and the women only wear black for formal occasions like anti-US rallies. Does anyone have an explanation for this?