I used Fiebings Mahogany Dye and went over it with a Fiebings Medium Brown Stain after it dried. One of the ways I've found to get the slightly molten coloring like on this sheath is to put a light layer of Neatsfoot oil on the sheath, let it soak until their's no more sheen and then put a healthy layer of dye. Allow to dry and then use the stain to even the tones out. There might be a better way, I've only been at this a little over a year, however, that's the technique I use.
Hope that helps.