Appearance colors have gotten goofy
Solution 1:
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?