If you ordered a retina mini you might want to check it for burn in. Multiple people are reporting their mini will retain images:

That was supposed to be a grey screen on the mini after a chess board was shown on the screen for a few minutes
more info here:
http://www.macrumors.com/2013/11/15/...ention-issues/
link to the test:
http://www.marco.org/rmbp-irtest.html