LCD monitor works on RGB, if color is red, you have lost blue, green or both channels. This can happen because of a bad video cable, then double check.
If the cable is OK, then test the ribbon cable to LCD, and the input signal board, where you connect the video cable.
If you do not find anything in there , then it is usually the LCD controller board, in that case you usually replace it after testing, as troubleshooting and repairing a complex board like LCD controller may be difficult.
You find parts for several monitor here :
Replacement Parts: Plasma TVs, LCDAlternatively order parts from manufacturer.