i was looking for ideas to make all different colors with ingredients that are
all natural for like
bergamont bath bomb
etc all the essential oils
People do not kine food coloring or any chemical
If you search the soap forums for "natural colorants" you will find a lot of threads, also look down at the links at the bottom of this thread. Alkanet root makes purple, madder root a brick red, french green clay an olive green, annatto a bright yellow, paprika for a red/orange, spirulina/parsley/dried spinach powder for green, indigo for blue.
I always infuse these with oil, so not sure how to use in a bath bomb - that would take some experimentation. Some you can add dry, but you want to watch out for staining. I have had good luck with soaking indigo, madder and spirulina in glycerin and adding drop by drop to melt and pour soaps.
For reference, the ingredients of bath bombs (citric acid, baking soda etc) ARE chemicals, you really cant make chemical-free anything