I'm not an expert on rear projection tv's nor common issues that arise with them, so this is a simple suggestion. It could be a calibration issue, although it's sudden occurrence as you suggest doesn't do much for that idea. However try messing around withthe picture settings, such as hue, colour saturation and see what happens. If there is a shift and the pink alters or disappears then you're in. But like I said, it could be a more serious issue to do with the actual projection.
If it is a calibration issue, you might as well grab a screen calibration disc if you want that can optimise and give you the best possible picture quality from your tv. But that's wish-full thinking, fist diagnose the problem.