I haven't got the faintest idea what is causing this issue, but hopefully somebody here has experienced it before.
When I haven't used my computer for a while I decide to wake it up from sleep by pressing a random button on my external keyboard. I have it set up so that the MBA itself is closed, i.e. the Thunderbolt Display is the only screen I am using.
The computer always wakes up immediately and most of the times it works just as expected, but sometimes the color of the display is shifted to a quite prominent purplish tone. When this happens I open and close the lid of the laptop, which immediately solves the problem, but I'm curious as to why the problem exists in the first place.
It started happening a few weeks ago and I have been using the MBA with the TB display since summer 2012.
Thank you in advance.
EDIT: Just took a screenshot which after opening and closing the lid doesn't show any discoloration, which leads me to believe this is a hardware issue. Added a picture showing how it looks.