Follow these tips if you plan on eating decorated hard-cooked eggs.
Refrigerate hard-cooked eggs whenever you're not working with them. Put them in their cartons if you won't be decorating them right after cooking. Refrigerate them again right after dyeing or decorating them. The American Egg Board advises that you discard hard-cooked eggs that have been out of the fridge for more than two hours.
Make sure the eggs you color aren't cracked. If any cracks appear during dyeing or decorating, throw them away. Also throw away any eggs that have been out of the refrigerator for more than 2 hours.
Use food coloring or specially made, food-grade egg dyes. Dissolve the dye in water that is warmer than the eggs. If you are using crayons, paints, or other art materials, be sure they are labled nontoxic. Or, use edible decorations like herbs. (You can use any art materials you like if you're not going to eat the eggs.)
To prevent discolored rings from forming on hard-boiled eggs, put them in a pan, add water to cover by 1 inch and bring just to a boil. Remove from heat, cover and let stand 15 to 18 minutes, then chill in cold water.
To dye eggs without a kit, add 1 teaspoon white vinegar and 20 drops of food color to 1/2 cup boiling water. Dip eggs.