The different hue thing exists, as to why I can not say. It may be combination of factors. Have you ever noticed the high proportion of Scottish guns which have plum tone to the blue?
We are pretty dry here in CO and humidity is certainly one factor that effects how aggressively the rusting agent reacts to the steel.
I had a completely different process I used at my old shop. I would turn on the tanks and close the door on my bluing room after coating the barrels with solution. It would get up to about as hot as I could stand it in there with 100% humidity. Within 10 minutes the barrels were ready to boil. Lots of short passes resulted in a very high luster blue.
I am happy with my current method but I am always tweaking things. I recently starting playing around with steam conversion. It has a place in my shop for sure.
