The rainbow (or gold, or black) finish available on your titanium frame is often mistaken for paint, or anodizing, or heat treating. It’s not any of those things, however. It’s actually a Physical Vapor Deposition (PVD) coating that electrically deposits a very thin, hard layer of titanium nitride (TiN) on the surface. This is done in a vacuum chamber with temperatures ranging from 350-800 degrees C. This results in a hard, corrosion-resistant, and low-friction surface. The coating is only a few microns thick, and takes on the finish of the surface beneath it. It can be polished to a high gloss, but since it is thin, it can easily be polished away as well. High wear areas on the frame should be protected with frame tape or other rub guards.
PVD finishes are actually very common in industry, being used for a wide variety of common things such as lamp fixtures and water faucets. The rainbow-effect finish, which is visually stunning, is actually considered a defective finish color by the industry, which is usually trying to achieve a solid finish of a particular color. Of course, our finish is intentional, and by the nature of the random variations produced in the vacuum chamber, no two finishes will ever be the same.