I think either your monitor cable is loose or your ATI card is defective. I have seen both these senarios at the office I work at.

Test1:Make sure the screws are tightened on the monitor cable and take a grip of your monitor cable while the computer is running with a pink hue and move it around a bit and at the same time check if the Pink dissapears or changes hue.(bad cable is common on "low budget" monitors)

Test2: this is little trickier and might not actually show a defect, open the cover of your computer and while checking the monitor hue(computer on) carefully bend your graphic card sideways and see if the hue changes. if the hue changes the card is bad and needs to be replaced. (we have had maybe 3-4 ATI cards that did this)

Other ways to test is try another monitor or Graphics adapter if you have access to these.

Good Luck /Thomas