Missing colors are almost never the result of monitors needing color adjustments, but a hardware issue. First, reseat the cables at both ends (video card and monitor), if that does not work, try another cable. If that does not work, try another TYPE of cable to rule out a bad port on the video card or monitor (DVI if you use VGA now, or DisplayPort, or something). Then try the monitor at another PC, if it works there after you tried different cables, replace the video card.