What type of Monitor are you using ?
As we don`t know i can only offer some suggestions.
- Make sure its set at True Color ( 32 Bit ) in the Control Panels Display settings.
Go to Start Menu.
Type in Display and select it from the drop down.
In the right hand pane select Change Display Settings and open it.
Click the blue link called Advanced settings.
Click the Tab called Monitor to make sure its set to True Color 32 bit.
- Try using the Monitors Function Buttons to change the Brightness and Contrast.
Try between the Natural / Warm @ Cool settings that most Monitors support within their function buttons.
- If using a installed Graphics Card make sure you have the Drivers Installed.
Some Graphics Cards support changing Brightness and Contrast in their Control Panel.
Still, i suggest you do this with the Monitors Function Buttons first to see if this sorts out the issue.
- You could also try the Windows 7 Calibrate Display Color.
Go to Start Menu.
Type in Calibrate display color and open it .
Click the Next Button down in the bottom right hand.
Follow its Instructions through to the end.
Hopefully this helps some what.