Go to the link, scroll down to the BLUE square (#5), and keep watching CLOSELY for 30 seconds or so... http://www.realcolorwheel.com/afterimage.htm Then move the gray top-bar of a webpage to the top left corner of your iMac screen. The gray bar should be a nice cool gray. Look at it for thirty seconds or so. Then move the gray bar to the bottom right. See the warm tone of the gray in that position? Almost yellow?. Now LEAVE the gray bar in that bottom right position. Then sit back and LOOK AWAY from the screen for one minute (looking away from any bright light). Then... look at the gray bar again, still at bottom right. Gosh! It's a cool gray! Of course, this is in no way intended to suggest that the yellow tint phenomenon is all a hoax.