I absolutely loved the soft pastel shades that this method achieved. If you want to try it for yourself, here's what you do:
Put a teakettle of water on to boil. While you are waiting, measure 1-1/2 teaspoons of white vinegar into five coffee cups.
Then add the following ingredients to the five cups (note: there was a sixth cup mentioned in Backyard Poultry's article using red onions skins but I didn't like the color at all, sort of a muddy purple gray, so I wouldn't do that one again)
Clockwise from top:
For lime green eggs - 1/4 Cup chopped red cabbage and 1 teaspoon turmeric
For purplish gray eggs - Papery peels from two red onions (I would skip this one next time)
For peach eggs - Papery peels from two yellow onions
For yellow eggs - 1 Tablespoon turmeric
For pinkish purple eggs - 1/4 Cup shredded fresh beets
For blue eggs - 1/4 Cup chopped red cabbage
Add a cup of boiling water to each coffee cup and stir to mix. Let sit until the contents cool to room temperature.
In the meantime, set up a drying rack. I happen to knit and decided to make a drying 'rack' using my blocking board (you could also use a piece of styrofoam). I covered the blocking board with papertowels,
and then stuck blocking pins into the board, four to a square, set apart to cup each egg while it dries.
After the cups have cooled, strain each one into another cup.
Then place a white egg into each cup ( I used white because I wanted light pastel eggs). I used uncooked eggs, but you can use hard cooked or blown out eggs also. Let the eggs sit for 30 minutes.
Take each egg out carefully and gently blot with a paper towel.
Set each egg onto the pins to dry completely.
When the eggs are dry, rub a bit of vegetable oil onto the surface using a paper towel and wipe off any excess.
~source for technique and inspiration Backyard Poultry Magazine April/May 2012 issue~