Can't go wrong with Sibley's book. I stain the throat and neck of my horns with brown RIT dye with a pinch of black. You will want to do this first before dyeing the body. I use an asparagus cooker, fill with water, dissolve the dye in the water and heat the cooker on a hot plate (or your kitchen stove) I let the dye work on the horn for 30 - 45 minutes or so. When dyeing the throat and neck, I put enough water in the cooker to just cover this portion. Once out of the dye I let the horn sit over night (I usually do this in the evening). The lower part of the body will be stained (can't help it) so you will have to scrape the dye off. The dye will have penetrated just a couple layers of horn. I will use some painters tape (blue tape) wrapped around the horn at the juncture of the body and throat while scraping. This will protect the horn if you slip (been there, done that). Now, I usually dye the throat/neck before I scrimshaw, for the reason that I have to scrape the horn after dyeing. Once I've scratched in the design, I ink it, buff off the extra ink, then final dyeing. I've tried several combinations of dye for the body, but now I pretty much use RIT tan. I like the look of that color. Good luck and let us know how it comes out...
Scott