An anodizing layer may be dyed or undyed. In the 8625 Mil spec, the term “Class” is used to designate this: Class 1 is clear or undyed, and Class 2 is dyed.
Anodizing layers are commonly dyed with organic dyes by dipping the part into a hot dye tank directly after anodizing. A wide variety of colors can be obtained through this process. By far the most commonly specified color is black, followed by blues, reds and golds. Note that only Type II anodizing can be dyed a variety of colors. Type III “hard” anodizing, which is quite dark even when undyed, is typically left clear or dyed black.
