I assume its your monitor or video settings
Heres a simple test I would do to check your colours:
Open Paint (aka MSPaint, In your startmenu, under accessories).
Using the rectangle tool, draw 3 boxes. Fill box one with red, box 2 with blue, and box 3 with green.
Those 3 colours should appear exaclty as their name says. If they are not correct, one of two things can be worng:
1. Your monitor colour settings are incorrect
2. Your videocard colour settings are incorrect.
To test your colours, the easiest thing to do is to plug your monitor into another computer that has working colours, and see if it shows up correctly.
If your monitor shows messed up colours on any computer you use it on, then your colour settings are incorrect, or your monitor has problems and needs to be serviced.
If your monitor shows correct colours on other computers, but not yours, then your colour settings on your videocard are incorrect.
To fix the videocard settings, I would recommend getting the user manual for your videocard, or if its a namebrand PC such as HP or etc, get its manual out and look in the index for video settings or a name similar to that.
Since every videocards settings are different, I cannot tell you exactly what to do to change the settings.