My 27" iMac 8gb 3.2 i5 AMD Radeon R9 in June and have been having problems waking from sleep for a while. if it is left to sleep for an extended period of time it will just self re-boot and/or the screen will turn green/blue as below, i could make this happen every time if i left the machine on for over 2 hours without use: After unplugging my second monitor (thunderbolt) this issue no longer happens (so far). My question is; why would the screen go this colour? Irrespective of the wake from sleep issue, is there a further issue with my graphics chip or logic board that i need to get addressed whilst im still in warranty? I have a Genuis bar appointment on Saturday but if the issue is fixed and there is nothing to worry about then id be glad not to pack away my mac and lug it 20 miles down the road. Any help would be appreciated. I have cleared the memory as requested by Apple Care.