Anodizing system under sulfuric acid at low temperatures and much higher currents than type II, commonly referred to as "hard anodizing", is used to protect aluminum materials under severe abrasion...

Colorless anodization? Being non-stained, the anodized layer can differ in color due to alloying components, with aluminum with less alloying content being less likely to change color.

Class 2 is kind of colored anodized surface with a variety of basic colors such as black or mixed, blue, red, yellow, orange, purple, green, ... PROPERTIES OF COLOR ANODIZING...