Preview App: adjust color tool is blank
In Preview, the Adjust Color tool is supposed to have a little rectangle where you can see the graph of the colors, and you can then slide the little houses at the bottom to play with the levels of an image.
Suddenly, the rectangle is all just plain white. The tool still works, but I don't have any visual reference. This has been going on for a couple of weeks. Can't tie it to any updates. It just started happening. Hasn't come back.
Any clues on how to restore it?