It's titanium dioxide, and it'll still appear after using a butane torch too, but butane only burns at 2500 degrees, so it doesn't happen as fast. Some people say its a protective layer that presents the Ti from oxidizing further, but I think it just made me wanna switch to quartz full time.
Titanium dioxide is highly inert, and once oxidixed and nitrated, the protective layer stops corrosion. Titanium, Zirconium, Gold, Chromium, Nickle, etc are all considered stainless, not because they don't corrode, but because they corrode very fast, but in a very thin layer, which protects the rest of the surface from further corrosion.
You can note that when breaking in Borosilicate or Quartz wands and nails, versus Titanium wands and nails. If it isn't pre-seasoned, the Titanium starts off with a strong metalic taste, but rapidly fades to no added taste, while the Borosilicate and Quartz will always add a hot glass taste.
The light grey ash that forms on the pipes, is from the hydrocarbons that are being dabbed on them. I routinely clean my Ti by superheating it so that all carbon is reduced to CO2, same is in a self cleaning oven.