Hi,
got a brandnew mini 2014 this August and it has been working fine, then suddenly within the last 7 days I had the problem twice.
Waking from sleep all colours inverted.
First time I woke it from longer sleep and got the normal looking login screen. Only that within the password field I saw strange colours as if looking through a small window slit. Submitted my password and wow everything inverted - me slightly in panic just decided to restart it and that solved it.
I checked Logfiles but no kernel panic, no major looking error messages.
Second time I was less in panic and first took a screen capture with 'Preview' saved it and then just logged out the user. It took more than double the usual time for the login screen to appear but that was in normal colouring again as was the screen after logging the user back in.
The screen capture I had taken shows a completely normal screen !
And again no unusual logs, messages or such.
I'm glad I found this thread, been working with minis for years through my job but this is the first I bought new and fitted for my personal needs and it would be heartbreaking if it had serious problems in the hardware. But reading all your posts I too am beginning to think it's a software problem.
If I find the time I'll analyse the logs more maybe there is something in common to the two incidents.