How do I color soap naturally?
Short answer
With clays, activated charcoal, spirulina, spices and macerated oils, always pre-dispersed first to avoid specks.
Explanation
The book covers kaolin (white), rose kaolin (pink), French green clay, rhassoul, activated charcoal (jet black), spirulina (green that shifts toward olive, sage or teal), turmeric (yellow-orange), paprika and cocoa (rust to brown), madder root (pink), annatto (orange), coffee, ginger and cinnamon, vegetable purées, and the golden color of calendula macerate. Mica and liquid pigment are used for melt-and-pour embeds.
Full gel intensifies colors; no-gel keeps layer lines crisp. Activated charcoal is a pigment, not a dye, so it won't stain skin, and gray lather is normal.
What to do
- Pre-disperse every powder in a little oil, glycerin or water before adding it.
- Add colorants at thin to medium trace.
- Cure spirulina soaps in the dark; it's light-sensitive.
Source: The Big Book of Homemade Soap — Fragrances and Colorants for Cold & Hot Process Soap · Natural & Functional Additives for Handmade Soap