It could be that someone was messing with the universal access settings, where there is a pane to control over-all display contrast. If you can get back to the afflicted machines, open up system preferences, universal access, and then note where the "enhance contrast" slider is. It should be all the way to the left, on "normal."
Well, I went to another store and the screens are fine there.
I played around with the universal settings, and a slight increase to the contrast is EXACTLY how those other ones looked. I'm pretty sure it must've just been this (you can also accidentally adjust it by hitting ctrl+option+command and either , or .
One day I might go back there and check it out, but as far as I'm concerned, it's case closed! Thanks.
I would normally think that someone messed with the display macs, but the fact that it was only on the MBA and MBP 15" (the two macs there with the 'nicer' glossy displays), I thought something was up.