This is frequently the result of a change in the contrast settings in
System Preferences >
Universal Access and can be "fixed" by pressing Command-Option-Control-Comma to reduce the contrast, Command-Option-Control-Period to increase the contrast, or even better, open
System Preferences >
Universal Access >
Seeing and adjust the
Enhance contrast slider to your preferred screen contrast. This option offers an opportunity for more precise fine tuning.
If this happens often and you suspect inadvertent activation of these keyboard combos, they can be disabled in
System Preferences >
Keyboard & Mouse >
Keyboard Shortcuts.
You may also want to check the settings in
System Preferences >
Displays. (Different OS versions may have different options.)
NOTE: Depending on your keyboard, your OS version, and various preference settings, the F keys or the fn+F keys on laptops may also control screen brightness (F1 dim, F2 bright) and contrast (F5 less, F6 more).
Written by jchuzi and joemikeb with contributions from dianne and dkmarsh in Using Enhance contrast slider / keyboard shortcuts.
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