Not much to it. I put some conditioner (white) in a foam egg carton, and added a bit of food coloring. I didn’t add too much coloring, so the color is somewhat faint, but I actually like the end result. The kids like the feel of it, and I like that it’s washable. And that they can play with conditioner under supervision. (I also like finding a use for a conditioner that I didn’t like on my hair…)
You can add spices instead of food coloring. However, FYI, cocoa is messier, and paprika or cinnamon can cause some irritation.