Background is gray or dingy due to magnetic charge build-up.
Cause:
When a display unit is running for a long period of time (many hours or days), it builds up a large magnetic charge that can cause a gray or dingy cast.
Solution:
Degauss display unit or turn it off.
Do one of the following:
1) Use the 'Degauss' button on the monitor (if available).
a) Locate the 'Degauss' button. Try one of the following locations:
1] Just underneath the lower front edge of display.
2] Inside a control panel door on the display.
3] Along the left or right side of display.
4] Somewhere on the rear panel of the display.
NOTE: For the exact location of the DEGAUSS button, consult the manual that came with the display.
b) Identify the 'Degauss' button and choose it.
2) Turn the display unit off. Wait one or two minutes (for magnetic charge to dissipate). Turn it back on.