I've used the red onion skins before. They render the most elegant mahogany eggs.

I have also negative printed ferns, clovers,etc. with red onion skins. Sacrifice an old pair of stockings. Cut squares of the fabric large enough to wrap an egg. Lay the leaf flat on the egg, wrap tightly with the cloth, fasten with a wire twisty tie. Then, boil in the dye made from the red onion skins.

When cooked, remove cloth, tie and leaf.

So, so pretty!