Homemade natural food coloring. There are lots of variations of this. A thinned down turmeric is a pale yellow, and adding vinegar or baking soda to red cabbage can change it to various shades of pink or blue. Hibiscus flowers make another pink, and kale or macha powder are more options for green. Artificial coloring is probably bad for you, at least if eaten too often, but these are actively good for you!
Learn how to quickly and easily make your own natural food colorings that are bright enough to make things like colored sugar crystals. This year I made colored sugar crystals for decorating some Easter treats, and I'll how you how easy it is to make them using your homemade natural food colorings.
Since it is my firm belief that nobody should EVER have to go through the expense, mess, or sugar high of testing different methods of turning icing red and green I documented it all and turned it into a convenient downloadable PDF.