The verdict is neither band is actually the natural color of titanium; rather, they are all coated with PVD. The white titanium and “natural” titanium variants just have lighter-colored frames to match their back glass. This means any scratches on the frame of the white and natural titanium iPhones are less likely to stand out compared to the black and blue titanium iPhones.
Having said that, a person posted on Reddit stating they had a natural titanium iPhone with a scratch on the frame, but was able to buff it out with some polish:
It’ll be interesting to find out if this only works on light scratches, and if it works on the white titanium iPhone as well.