Does anyone know how to change the colors of the zhu zhu pets?

I've seen the zhu zhu pets in all different colors on ebay and was just wondering if anyone knows what people are using to change the colors, I've seen purple, green, blue, pink, red, and some are like tye-dyed so I'm wondering if people are using dyes they state that whatever they are using to change the colors is non-toxic. I would like to know so that I could make some for a sick friend that is collecting them so any instructions on how to do this would be greatly appreciated. Thank youDoes anyone know how to change the colors of the zhu zhu pets?ko