It's so much fun to decorate cakes and cupcakes to make them colorful and unique. It is not very professional, though, to show up at work with blue hands (not to mention a spot on your chin) the next morning. You have to remove those unsightly food coloring stains.
First, wash your skin with soap and warm water. In this case, all soap is equal, it is not likely to remove the stains completely. If you have food coloring stains on your face, wash it with a gentle face cleanser that you normally use. Using harsh soap on your face could cause skin irritation, especially if you have sensitive skin.
After washing, dry your skin lightly and apply a dab of toothpaste. Rub the skin with your fingertips. For deep stains on your hands you can use a nail brush. Toothpaste is one of the best food coloring removers. I used Colgate Advanced (that's what I had at home), but any toothpaste should do the trick. Then, wash your skin again with soap and water. Unless you miss a spot, repeating the treatment won't be necessary.
Other common household items that are quite effective in removing food coloring stains are shaving cream and baking soda. Shaving cream is rather gentle on the skin and gets the job done. Baking soda may leave your hands a little dry and you may need some lotion, but it probably shouldn't be used on the face.
There are also other chemicals that can be used for removing stains from your hands, but shouldn't be used for face. One of them is Permatex Hand Cleaner, a professional hand cleaner in the form of paste that removes some of the toughest stains. Even Comet powder (or gel) will do the trick, but it is really not necessary to use such harsh chemicals on your skin since there are other, a lot more gentle ways to clean it.
If the stain is deep and despite several attempts it is still there, you might try a pumice stone (on hands only!). Pumice stones are natural solidified lava rocks and are widely used as foot care items. They are excellent for removing dry, rough skin from feet. However, you should be careful using a pumice on your hands, as it may literally remove the outside layer of your skin.
The best way to prevent stubborn food coloring stains on skin is to wash your skin with soap and water as soon as the stain appears. It will prevent food coloring from soaking deeply into your skin.