Historically, CRT monitors used to have separate red, green and blue intensity adjustments to cope with the fact that the separate guns age at different rates. The potentiometers for making these adjustments were sometimes made accessible without removing the case, sometimes not. In any case a large busy IT department might well decide that a monitor with degraded color balance was due for replacement, as it was not considered cost-effective to do the adjustments manually.
More recent models had a microprocessor to handle control and setup, and some Sony Trinitron monitors, including Dell badged ones, featured "digital color return technology" which was intended to enable a return to original factory-shipped color temperature and luminance if desired at any point over the lifetime of the monitor.
The operation needs to be performed with the guns warmed up, and it is locked out for about 10 to 20 minutes after switch on. During this time an "Available After Warm up" message is displayed if Color Return is selected using the OSD menu. After this time use of Color Return is possible.
One way to tell if a Trinitron monitor had microprocessor control was to see if Color Return is a menu option.
Obviously, if the tube is too far gone, perfect balance and luminance will be impossible to restore, but even with quite old kit, 7 to 10 years, people report acceptable results after using this feature.
I have heard stories of people who know about this retrieving Trinitron monitors from dumpsters because university or business IT departments have replaced them for being "too red" (or blue or green) because they were not aware of the Color return feature.