First, reset it to defaults. There may be some presets in the monitor you can try, first try those. They are often called Movie, Game, Bright, etc... If it's an older monitor the backlight may be failing which will change the clolors.
There is contracts and brightness for the main adjustments and you can also change the color temperature in most monitors, try different settings and see what you like.
Changing type of input used if you can may help.