Hi,
Have a 27-inch, late 2015, iMac and noticed when it wakes from sleep (overnight) there is a tiny horizontal multicolored band across the top of the screen. This just started maybe two days ago.
Any ideas?
mine was starting to get really strange. the gray is the edge of the browser and I took it to the Apple store Monday because after restarting the screen looked like a multicolored screen saver, lol. did all the hardware tests and nada. I was also having random restarts. got it back a few hours ago and they said the 3rd party ram was failing. got new ram and after a few hours, it's okay but I can't help but wait, lol.
make sure you take pics of the strange stuff in the future. hopefully, it was just a one time thing.
Thx.