Are the colors "off" on the screen? Do you have problems with images being too dark or too bright?
There a number of different reasons why your monitor may not be representing color properly.
Check the cable between the monitor and the computer to make sure it is secure. Each end should be tightly fastened.
Degauss the monitor. This will often help correct discoloration issues near the edges of the screen.
Reference the monitor manufacturer's instructions to adjust the brightness and contrast settings. If available, you may also need to adjust the color balance and temperature settings.
Adjust the color quality setting for the video card. This will often help resolve issues where the colors, especially in photos, appear incorrect.
If you have access to another monitor, try it in place of the one with the color issues. If the problem goes away replace the monitor. If the problem duplicates on the new monitor there is most likely an issue with the video card.