Yes, that's right, perspiration!
Apparently, the sensors of the newly updated liquid detection scan system (which already reminds many of us uncomfortably of the dystopian future presented in "Total Recall") are set so sensitively to any form of liquid that a southern heat wave is leading to nearly all dark clothed passengers receiving patdowns!
The message is clear. If you want to fly and you want to wear black, you better get yourself delivered to the airport in a refrigerated container truck! (And, of course, much like a weight watchers meeting, make sure you empty your bladder before you get in line, because who knows how deep they're looking for liquids!)