Sometimes we get so tired or dizzy, we see spots. As a person of the older persuasion, I sometimes get little flashes, a side effect of the natural process of aging (that I have, yes, consulted with my optometrist and general practioner about). But red squares? That’s a warning sign—but not about your vision.
A Macworld reader and a number of people across many forums over the last several years have found that their Mac will begin showing red squares for no reason they can determine. Some people see small red squares at random across their display; our reader and a few others have it happen only when they use QuickLook, the Finder and Open dialog preview method of selecting an item and pressing the spacebar to get a glimpse of a file’s innards.