Every sight I go to talks about hard coat, color, wear, and so on. So here is my two cents. If back in the early eighties you walked into a little two man shop in South Porland, ME known as Quality Parts (aka Bushmaster Firearms) you would have seen the armorer spray painting the lowers with Gun Kote and baking them in a toaster oven. No **** So anyone that owns a class III from Sendra or any lower that came out of that shop, that is what you got. Sounds pretty cheap but my sendra has held up well over the years of full auto abuse. Later after they moved out to Wyndom, ME I bought another lower that was hard coat anodized that looks as nice as the day I bought it.
Also has anyone ever thought about trying black walnut hulls boiled in water as dye. When I was a kid I used this to dye and prevent rust on steel animal traps. I would boil water on top of the wood stove in a metal five gallon bucket and drop in a dozen black walnuts still in the green hulls. Then dip the traps and let soak until they were as dark as I wanted them to be. The color stayed on the metal really well just don't get it on your hands I don't know of anything short of time that will get it off.