Can you change your hair colour without chemicals?

The chemical that you usually dye or bleach your hair with is hydrogen peroxide. Now interestingly, that's a typical reaction that you do in school. Hydrogen peroxide decomposes into oxygen very very slowly, but if you add something like potassium iodide you can make this happen a lot more quickly. There's a fantastic experiment you can do where you put some hydrogen peroxide (also found in contact lens fluid) and add a little bit of potassium iodide and bubbles. The whole thing comes sweeping out of the top in this big fountain of bubbles. As for trying to dye your hair without a catalyst, I'd go for the catalyst way myself!