I don't know what I did, but my screen colors are off base — menu bar has a peach background and window title bars are something like lilac. Colors within any menu vary from blue to peach.
In System Preferences > General, I changed appearance and highlight color from blue to graphite, which changed nothing. But when I booted off a backup disk for some maintenance, the colors were as they should be.
My guess is a preference file is corrupted. Booted off the backup, I copied all the "com.apple . . ." preferences to my regular startup disk, replacing. Booted off the regular disk, no change. It must be another preference file, and I have no idea which one.
Anyone suggestion?
This is a 2009 iMac; OS is 10.11.6.
Best Answer
One possibility is that you have inverted the colors. In 10.11.6 I believe you might do that accidentally by pressing Command-Option-Control-8 at the same time. Try holding down the command, option, and control keys with one hand and pressing the number 8 key with your other and see if that fixes the color scheme.
Another possibility would be to look at the color profiles in the color tab of the Display section of System Preferences. If there are multiple profiles there, does changing profiles fix the problem?