How Dangerous is Red or Pink Mold?

I would say that you actually have little reason to be concerned in this case, thankfully. Mold is transmitted by spores, which considering the enclosed nature of Tupperware, as well as the low temperature of the fridge, means that there's fairly little chance that it managed to spread. This being said, if you see red mold begin to spread to other, fresher, food items, you may need to empty out your refrigerator and sterilize the interior. Good luck, and clean out you fridge.