If there is no color on your computer display, one of the screen contrast effects in System Preferences may be turned on.

There are two screen contrast effects: "White on Black" and "Use grayscale."

To return your screen to its regular appearance, make sure that both of them are turned off.

To turn off the contrast effect:

Choose Apple menu > System Preferences, and then click Universal Access

Click Seeing.

Make sure "Black on White" is selected and deselect "Use grayscale" if it is checked.