While the dyes are simmering, prepare the eggs. Soak the herbs in a little water to help it adhere to the egg. Gently apply the herbs to the egg, making sure it sticks to the shell.
Tightly wrap a piece of cheesecloth around the egg, careful that all the herbs stay in place. Twist the cheesecloth tightly at the bottom and tie a knot of thread around it. Make sure everything is tightly secured for the best results.
Cut off the excess cheesecloth right above where you tied the knot. Repeat the process with all the eggs.
Once the dyes are cooled, gently lower half the eggs into the onion skin dye and the other half of the eggs into the blueberry dye. The eggs should be fully submerged in a single layer, and if they're not, use a smaller pot.
Bring the dye mixtures to a boil and then reduce heat to a gentle boil. Now set your timer for 10-12 minutes.
When your timer is up, gently take out the eggs with a slotted spoon and set them on a cooling rack or paper towels.
Cool the eggs for five minutes, then peel off the cheesecloth and herbs, while the eggs are still warm (otherwise the herbs will dry onto the egg and it will be harder to peel off).
Optionally, shine the eggs with a little olive oil to make their color stand out even more.