Did you try to twist the signal cord near the plugs? both on video card and on monitor?
90% of such malfunctions are caused by a break in a VGA cord or bad contacts in the plugs. VGA uses an analog signal, with separate lines for every of three colours. You can also try to reverse the signal cable. Also look at the pins in 15-pin VGA plugs, some of them may be bended.
If your OSD shows normal colours - it is probably something outside the monitor.