Actually, some forms of Indigo are approved by the FDA as a colorant, although you need to make sure you're using an approved one if you're going to list it as a colorant. The same holds true of other non-approved colorants that might be approved for other uses, such as food, but not as cosmetic colorants. Those of you using natural colorants need to make sure they're FDA approved colorants before listing them as colorants. They can be listed as additives, but not colorants. Otherwise your soap or B&B product is adulterated/misbranded. There are some clays that fall into this category, too.
FD&C Blue #1 comes from Indigo, btw.
Inbal, I use freeze dried Indigo crystals. Indigo needs to be added to hot water, (that's been measured for lye water) mixed well and then let the water
cool before adding lye. It doesn't take much Indigo. Approx. 1/4 tsp for 5 pounds of soap. I don't know what you're using, but that's what I use and do. Good luck!