My computer's monitor and TV look discolored and dark every time I turn it on after long intervals?

Every time I turn on my computer or TV after a gap of an hour or two,it looks discolored and dark.It especially happens when I turn it on in the morning just after I wake up.There is nothing wrong with its working.It works normally and gradually when I leave it on for half an hour or something it gets bright and comes back to its normal settings.Why is it happening ?What are the possible causes ? what should be done to get it repaired ?Has it got anything to do with electric fluctuation or regular power cut-offs ?