Colour means nothing. Most engine reconditioners will paint the engine to make it look nice, and use whatever colour they like.
I have seen a gold block, think it was on a diesel, don't know what or if it means anything at all, but it was a good runner, and had a copper fuel tank on it too, wasn't mine though, was sent to the scrappy the chassis was fubar
gold engines/blocks were the old bmc/brit leyland recon engines.
seem to rember you could get silver and gold seal, mind you was along time ago.LEEgold engines/blocks were the old bmc/brit leyland recon engines.