Your monitor should have basic colour/contrast/brightness controls, firstly calibrate them using a calibration card, like this one -
http://www.tldseller.com/HD%20TEST%20PATTERN%20LOGO.png
Following that, IIRC you have an ATI GFX card using Omega drivers, so navigate through to the Display Properties > Settings > Advanced, there you should saee the available options for the Omega display drivers, choose (IIRC) Colour and there you can change your Gamma levels. Click Apply/OK.