Hob coating is yellow. If the coating is darker, more parts will be made, and vice versa. Why?

Hehe, it doesn't mean that the darker the color, the more parts you make. The thicker the hob coating is, the more workpieces will be machined, but the coating cannot exceed 10μ in the end. At present, high-speed cutting hob generally uses AlTiN coating or CrAlN coating instead of yellow tin coating.