This was so simple I wish I had known about this when my kids were little.
Put a container of Cool Whip in a cake pan. Dot with several different colors of food coloring. Swirl the color around with a tooth pick, not too much though or it turns laundry lint grey. We wore gloves for easy clean up.
Roll the hard boiled eggs in the Cool Whip until they are completely covered. Let sit for 20 minutes.
After 20 minutes, take the eggs out and gingerly rinse them in a bowl of water so as not to disturb the color. Allow to dry and they are good to go.
Give the leftover Cool Whip to your chickens.