We call onion skins the gateway dye...accessible, cheap and user friendly for all dyers. Onion skins will yield golden yellows to greeny yellows depending on the variety. Our skins are a blend of a variety of onions and tend toward the warmer side. Pretty potent, onion skins will give deep shades at around 20%.
To dye, either put the peels in a muslin bag and use as a tea bag, or simmer for an hour before straining and adding fiber.