It takes a while and you might forget to go back, like I did. In the college of winterhold there is an apprentice mage, Breylana Maryon, if you let her experiment on you and your screen turns green, you have to leave and wait for it to 'go back to normal' but it just had the faded appearance. I read online that it could have been a corrupt save file or some sort of modified file in the, but there is the possibility that it may be from an incompleted quest, or so this was the case for me. For a while I had a blue faded tint to everything and couldn't pin down what the issue was, I tried the ethereal shout thing and it didn't work.