We created marbled eggs yesterday. :)
To create the marble effect, (Which turned out more like a speckled egg, really) just add 2 tablespoons of cooking oil to the egg coloring. Mix the oil into the water vigorously immediately before lowering an egg into the mixture. Leave the egg in for at least 30 seconds, remove it and add it to another color.
Kind of fun!
To make sure we didn't get our eggs mixed up, we used crayons to write names on the eggs beforehand.
The only thing I didn't like about the oil was that I had to clean the eggs off afterward. I let them sit for a few minutes so my cleaning wouldn't wipe too much of the color away.
The kids each dyed two eggs. They fit nicely into snack sized ziplock bags. Easy peasy!