Different grades of blade steel may look identical — a piece of ATS-34 looks the same as a piece of 8670M. To help you tell them apart, each product line is assigned a unique color code.
The color is a physical paint marking applied to the steel so you can quickly identify the grade, especially when you have multiple pieces in your shop.
The colors are arbitrary identifiers — they don’t indicate quality, hardness, or any other property of the steel itself.