Titanium anodization color spectrum - photo

[nova_robotics]

It's very interesting that it goes gold -> blue -> gold -> blue -> gold. It's super obvious we're just cycling through wavelengths as the oxide layer grows in thickness. Extremely cool.

MrTitanium.com How Titanium colors work without dye?

I'm not 100% convinced of this explanation because I believe that should cause the colour to change based on the viewing angle. But I think it's mostly right.