Self-colored" is just slang for "plain" or "unfinished" or "no plating or coating". Further, this piece of slang seems to never have found its way outside of the chain industry. Google "self colored finish" and you'll probably find no other references except to chain.

What does Self colored chain mean?

The term “self-colored” simply means the chain does not have a finish or coating on it.

Is zinc chain strong?

A great general purpose chain. Grade 70 Transport chain is a high strength, heat treated chain offering greater hardness and ultimate durability. ... Zinc Plated (E): The zinc plate is a very thin cosmetic coating of zinc deposited on the chain. This finish offers limited corrosion protection.