Red Onion Skins - our personal favorite, yields the dark mahogany colors. You can use the same dye bath a second time with another dozen eggs to achieve the lighter russet shades. We usually just boil the eggs and the onion skins together so that we are hard boiling and dying at the same time. You can find instructions and photos at our post called Eggcitement.
Turmeric - gives the very cheerful yellows
Red Cabbage leaves - Dyes eggs the blueish shade
You can also use: Black Tea (beige), fresh or frozen Spinach (green), fresh, frozen or canned blueberries (blue), canned cherries with juice (pink) and many others.
If you don't want to boil the eggs and the dye together - the other option would be to make a liquid dye. You can do this by Bringing 1 quart of water to a boil with up to one or two hand fulls of plant material. Once it is boiling, reduce the heat and simmer for 15 minutes or up to an hour until you achieve the color you like. Strain. For each cup of liquid dye add 1-2 Tbsp. white vinegar to set the color. Place your prepared dye bath in any glass container leaving room to add your already hard boiled eggs you wish to dye.
Have fun dying eggs the old-fashioned way!