I'm wondering how fine the colourants are that you are adding. I've seen many soaps that have small specs of the plant material. IDK if this is desirable for some of you but for many of mine I want no specs. I've used a food processor to powder the flakes and pass it through a very fine strainer (tea strainer) and it still seems a little large (probably less that .5mm). I found that the processor creates a super fine dust that should be very good for colouring (will show pics soon). I got this by leaving the spout of the food processor open and putting a bag over it with a rubber band sealing it around the spout. The dust is blown up and settles in the bag. I'm guessing a little will go A LONG way.
You should be able to do this with any plant material I'm guessing like paprika and others.
You should be able to do this with any plant material I'm guessing like paprika and others.