Display problem

[Simon Meyer]

I booted my cube this morning to discover everything displayed in 
negative?
It boots up with normal coloring, then goes to negative when I reach 
the desktop. The monitors panel reports colors as being set to 256.
Even when I change it back to millions there is no change. Rebooting 
makes it default back to 256.
Is there a preference I can delete to alleviate the problem or should I 
be looking somewhere else?

Thanks for your help - Simon