Taylor,
Over the years of using Kasenit, I have gotten much the same thing. After the quench in brine, the surface of the part is covered with a dark, not-to-adherent coating that comes off easily with a powered wire brush leaving a pleasing grey finish. And the part is hard. I think the "ugly color" Bob mentions is just a tough oxide layer. The primary constituent in Cherry Red and in Brownells surface hardeners is, of all things, potassium nitrate !!! So I think the operative mechanism is that the melted KNO3 is imparting a certain amount of nitrogen at temperature to "nitride" the steel surface. However, since potassium nitrate also contains a large percentage of oxygen, it contributes to the hard scaling that Bob is talking about. The sodium ferrocyanide has no oxygen but contains only sodium, iron, and triple bonded carbon / nitrogen. So you get a nitrocarburizing processes.....both carbon and nitrogen are diffusing into the steel surface to harden it. By just mixing the Brownells stuff with the sodium ferrocyanide there will still be KNO3 present, but not in the same concentration. I'm betting the hardening will be much improved but I will find out if the KNO3 still leaves a heavily oxidized / scaled surface.
Will keep you posted.