iMac Retina 5k Display Has Marks Behind Screen. Why?
I have a new 27-inch iMac with Retina 5k Display. On the screen, above the Trash can in the lower right corner, are a few dozen or so 'marks or smudges' that appear on the screen, most easily seen with the Finder open. The marks are visible to the eye, but do not show up in a screen capture so they're not related to OS X, and they appear visible behind text, photos, or lines in the finder; almost as if they're a smudge from a marker, or someone tried to wipe the actual screen with a dirty rag. Visibly, they're annoying, but are not captured by any screen grab.
Any idea on how the marks got there and how to get rid of them?
The marks are not on the front of the display, but appear to be behind whatever OS X displays on the screen. It does not matter what is on the screen, including app, desktop wallpaper, Finder-- the marks are always visible (unless the image is of a similar color).
iMac with Retina 5K display, OS X Yosemite (10.10.2), 24GB RAM, i5 CPU