Anodizing helps to resist corrosion, increase surface hardness, improve wear resistance. This process serves both functional and cosmetic purposes. Anodizing is less expensive than painting, with the exception of coil painted products. The typical coating thickness: 12-18 μm for black, 8-12 μm for clear, 4-8 μm for color. Anodizing also known as hard anodizing, provides excellent corrosion and wear resistance, suitable for functional applications, but is more limited in color—often clear or black only. The typical thickness 30-125 μm.
Clear anodizing is a way to anodize metal that produces a clear finish, and it is one of the simpler and easier anodizing ways to do.Clear anodizing is typically a sulfuric acid anodizing process, and as a result, offers better wear resistance than chromic acid anodizing and comparable corrosion resistance. It is done by placing the Aluminum or another metal is placed in an acidic electrolyte; this usually is from sulfuric acid. An electrode then causes the acid to lose its oxygen molecules, which are adopted by the metal. This adds a new layer to the clear anodized metal.  After the acid bath is finished, the metal is quickly dipped in hot water to seal the layer and make it permanent.
This commonly is done in a variety of applications, clear anodizing benefits diverse industries including: architecture, for use in window and door frames, railings and siding; automotive, for use in trim and housings for various exposed parts;  printing, for use as commercial photolithography plates; and industrial manufacturing, for sheet metal and various extrusions such as profiles and cases for additional surface protection.
While clear anodizing also can be dyed, this must be done quickly and right after the acid bath. The disadvantage of this method is that the oxide layer is not as strong as other methods, so this metal can rarely be used for building or engineering.

Color anodizing is the process of anodizing a metal and then adding dye to the metal before it is sealed. In anodizing, the metal is placed in an electrolyte tank and an electric current passes through the electrolyte to form an oxide layer.   After the oxide layer is formed, the dye can be applied to the metal, depending on the pore size of the metal.   Aluminum is the most commonly used metal in color anodizing, but several other metals can be used, including titanium and magnesium.   Although anodizing has several important benefits, color is added primarily to help distinguish parts and make them look more suitable for consumers.  After the completion of conventional anodizing, the pore density of the metal will change.   Metals can be given different colors depending on how long they have been anodized, the metal, and the method of anodizing.   The dye is added directly to the metal, and the color adheres to the metal like the fabric.   If the metal is not anodized beforehand and then the pores are too small, the dye will run off the surface of the metal.   Only certain metals can be used for color anodizing because these metals must react freely with oxygen.   If they do not react with oxygen, then the oxide layer does not form properly and cannot be stained.   The two most common metals are aluminum and titanium because of their hardness and anodizing other metals outside of general use include zinc, tantalum, and magnesium.   Unlike conventional anodizing, which has some mechanical benefits, color anodizing is primarily used for cosmetic purposes.   The dyed metal will still gain mechanical benefits, such as increased surface hardness, but metals are rarely used for this.   Color anodized metals are commonly used to help distinguish the color of parts, making metal products more visually appealing in consumer goods and clothing jewelry.   This process produces less pollution and less leftover material than other dyeing processes.
In fact, you can add any color you like to anodized aluminum parts. Coloring is accomplished either by using dyes during the anodizing process or by painting afterward. Dying is preferred, as it creates permanent coloration which means it won't fade and can't be scratched off.