If your display doesn’t look right
If the image on your display doesn’t look right, try one or more of these suggestions.
If the display is black or dim: Try adjusting your display’s brightness.
If images are too large or too small: Try adjusting your display’s resolution.
If the colors don’t look right: Try using the display profile designed for your display. For example, if you are using a Thunderbolt display, choose Apple menu > System Preferences, then click Displays. Click the Thunderbolt Display window, click Color, then select “Thunderbolt Display” from the Display profile list. If that doesn’t work, try calibrating the display.
If your display is garbled: Make sure your Mac has detected that display. Choose Apple menu > System Preferences, click Displays, then click Display.
Then click the Detect Displays button. You may need to press the Option key to see the Detect Displays button.
If the display is flickering: Make sure your Mac and display are connected to one another with good quality cables and adapters. You may also be experiencing interference from a nearby power line, a fluorescent light, a radio, a microwave oven, another computer, or another electrical device. Try relocating nearby electrical devices or moving your Mac and display.
If you see bright or dark spots on a flat-panel or portable computer screen: Your display may have pixel anomalies. If you suspect your Apple display contains a high number of anomalies, take it to an Apple Authorized Service Provider.
If none of these solutions work: If you have an Apple display and can’t correct the problem, contact an Apple Authorized Service Provider for more help. Don’t attempt to repair the display yourself, because any damage you may cause is not covered under your warranty.