Canon's had a bit of a manufacturing screw-up, it seems: a small batch of the company's brand-new EOS Rebel T4i / 650D DSLR cameras have rubber grips that include an unwanted chemical that could change their color from black to white, and potentially cause an allergic reaction as well. Canon says that too much rubber accelerator was used to vulcanize the rubber grips, and a light coating of Zinc dimethyldithiocarbamate was the result. Also known as Zinc bis or ZDMC, it's a chemical which has been known to cause light skin and eye irritation in some cases, but won't necessarily do any harm.
According to the company, only cameras manufactured between May 31st and June 15th are affected, although those units may have been shipped around the world, as both Canon US and Canon UK issued advisory warnings about the problem. There's an easy way to check: if the sixth digit of your serial number is a "2" or above, you're in the clear. If it's a "1," you can enter the full number at this link to see if your DSLR is eligible for a free repair, which should be available sometime next month. In the meanwhile, Canon advises you to wash your hands after touching an affected camera.