Perhaps the contrast 'fools' the eye; maybe in a manner similar to those drawings that you have to stare at for a few seconds in order to discern a secondary or tertiary image?
'Course, on a thermal imager, it altogether too easy to spot a person up and walking around.
I'm guessing that one area of intense military research is in the arena of garments that mask the wearer's heat signature. This would be great until you're injured or in trouble in an unfriendly zone and need a ride out. Not giving off a heat pattern gives rescuers one less tool to help them find you.
On a semi related side note, we 'lost' a trooper in the back of the NWTC, past Mississippi Range. An AC-130 was in the AO and was able to spot the man in just minutes. I hope the one flying for the My Hood operation can find the missing climbers.
Let's all hope and pray that they are found safe. A note left behind indicated that they had ample supplies, but an injury or a particularly vicious storm can make all of that pretty meaningless.
If they were able to snow cave up with their supplys. They should be able to ride the storm out.