You can dye egg shells different colours if you hard boil them in water with different things in it. (but I wouldn't eat the eggs afterwards! Below is a list of what things turn the shells different colours.
Spinach Leafs = Green
Beetroot = Red
Tea Bag = Dark Brown
Onion Skin = Yellow / Gold
Red Gabbage Leaves = Light Blue
If you know of any others, please let me know!
Please only try this with some adult supervision!!