iMac display turning sepia tone

My iMac display [2.5 GHz Intel Core i5, 21.5-inch, Mid 2011, OS X 10.7.5] turns a sepia tone by itself after several hours of use.

When I wake the computer in the morning, it may have a sepia tone, but will transition to a regular screen within about a minute and then after use may (or may not) gradually take on the sepia tone again.

Ummm, anyone have any idea of what's what here? The Universal Prefs appear to be as they should be.

The only way to tell if the problem is with the LCD itself or the graphics chipset in your iMac is to attach an external monitor and see if the same thing happens. Your iMac is equipped with a Thunderbolt video output connector which is backward compatible with MiniDisplayPort. You'll need the proper adapter and cable to attach an external monitor.

You can always take your iMac to Apple and let them diagnose the problem. If you take it to an Apple store genius bar, they will not charge you for the diagnosis but of course will if you decide to repair it. I'm assuming your iMac is out of warranty.

Thank you for this. I will try to mirror another monitor to explore the situation more fully before I go Apple for possible repair. The computer is still under warranty.

Thanks again.