Brake shoe color coding

[tree98]

They put different colors on the edge of brake shoes. Green, red, blue, yellow. I think this is an indicator of the lining on the shoe. Like red is 22,000 lb. Green is 20,000 lb. Or maybe it's the other way around? I googled this and couldn't find much. What do the different colors stand for?

[Rockhwy]

Not all replacement brake shoes are color coded by colors but are rated by weight such as 23000 lb or 20000lb and by what kind of operation the vehicle is involved in.