Personally, I think it was a gimick to compete with the "corrosion resistant" Ruger Mini-14 Stainless Ranch.
Ruger was pushing their Stainless Mini to charter fishing and dive operators, pleasure craft owners, and others in the Florida area due to some piracy/drug smuggling issues off the coast. Legitimate concerns. Colt and Ruger weren't the only two, Winchester came out with their Winchester Defender, Stainless Marine, in 12G., in about the same time frame.
It does not shoot any different, but I have never had any surface rust on the barrel or FSB at all, In fact, no rust at all except very minor surface rust for the non-coated parts. Swamp coolers and guns just dont mix.
Still, it was just different enough, hanging on the wall in a sea of black rifles, that I had to have it. 22 years later, it still puts the bullets where I want them to go.