A couple of things come to mind when I look at the photo. There could be an issue with the white balance control that might be resolved with recalibration.This is a little involved, but is detailed in the owners manual.
Do you use Auto White Balance, and if so, have you tried a custom white balance to see if that helps? What I suspect though, is the flash bulb might be at fault here too. It looks like the temperature range of the flash bulb might have changed through weakening of the flash unit. This could be from a battery that is old and lacks sufficient voltage to fire the flash at the right value. Unless of course you don't use flash, in which case the sensor or processor could be at fault. Since sensors are pretty rugged, I would suspect the processor first. You don't mention if you shoot in RAW or not, so I'll assume you don't. Try shooting a few photos in RAW format since this won't use the processor of the camera. see if the photos look better. If they do, then the Digic processor is most likely at fault and would need to be replaced. If the results are the same in RAW as JPEG, then the sensor might be the issue. Either way, the camera would need some attention by Canon service center.
Steve M.
