Nurture should be able to give you the INCI name for a colorant. Often times it's listed right in the product description. Sometimes there's a link you can click to read the tech info for the product.
For example, Nature's Garden 24 karat gold mica has an INCI of Mica, titanium dioxide, and iron oxide. That's in order from most to least. One of my soap recipes includes this mica as a top decoration. The ingredients list for this soap is:
Lard, beer, high oleic sunflower, tallow, coconut oil, sodium hydroxide, avocado seed oil, fragrance, potassium hydroxide, tetrasodium EDTA, cocoa powder, mica, titanium dioxide, and iron oxide
For ingredients under 1% of the total, you can list them in any order, at least in the US. In this example, I know tetrasodium EDTA, cocoa powder, and the gold mica are under 1% of the total. I also know for sure the EDTA weighs more than the other two, so I choose to list the EDTA first to play by the rules as best I can, the cocoa second because it's more interesting ingredient and probably a little more "user friendly", and the more esoteric mica INCI last.
This is what's called "what goes into the pot" method of creating an ingredient list and this is okay for US soap makers. If you are not in the US, you may have to list ingredients that are actually in the soap after saponification. Your colorant would still be listed by INCI name, but your other ingredients would look different. You'd list the soaps created -- sodium lardate, sodium sunflowerate, etc. -- in order, from most to least, as well as the glycerin created by saponification. All of these names would also need to be official INCI names, not the common names as you would use in the US.