Prepare a dye bath in a small heatproof mixing bowl: Mix 1 teaspoon of vinegar and 20 drops of food coloring (use more to intensify color) with 1 cup of hot water. Add an egg, and submerge it until it turns the desired hue. Remove egg; let dry, about 15 minutes.
In a shallow, wide bowl, prepare another batch of dye in a darker or different shade; this will provide the swirls. The liquid should be 1/2 inch deep. Add about 1 tablespoon olive oil (you may need more depending on the size of the container). Run a fork through this mixture, creating swirls of oil on the surface. Place the dyed egg in the marbleizing mixture, and roll it once around the bowl to pick up the oil streaks; remove, and blot gently with a paper towel. Let dry, 30 minutes.
Try various color combinations. Vary the base tints and the swirls to achieve contrasts both striking and subtle.