The color on a user's display is strange. It was perfectly fine yesterday. What is the best course of action in this situation?

The strange color on the display indicates a loose cable. Check both cable's ends to see whether they are seated properly. You should also try turning the display or the PC off and back on or check to see if someone has bumped or modified the display's settings. If none of those solutions worked, you would next try a known good display on the computer. If the problem persists, it's not the display. Perhaps it's time to purchase a new graphics card.