Most of the time I have a handle on what is going on with my iMac.........if not I ask questions here on the forum. I noticed what I believed to be burnout pixels about 18 on my screen so made an appointment with Apple service. Took it in to the store, waited in line for my appointment time. Put the iMac on the service desk and the tech looking at the screen, pointed to several of the blue and red spots on the screen. Said is that what you are having trouble with? He then pickup a cleaning cloth and wiped them off. Said it was oil of some kind that had gotten on my screen. I never even thought of wiping those spots, just believed it was some burned out pixels. Felt like a fool and deserved the DAH award for the year. Live an learn the hard way, maybe this will help others who think as I did. Still don't know how the oil spots got there. So have a laugh on me.