I was planning to do a natural dyes (cabbage, tumeric, onions) but I ended up being short on time for the boiling step, so I went for food coloring. 20 drops + 1 teaspoon vinegar + 1/2 cup boiling water---easy peasy. And while plastic cups may seem like a good idea, they knock over so easily. Just use heavy glass tumblers or mugs. The dye will come out, I promise.