[Footkerchief]

I always assumed it was some kind of bacterial product from early spoilage. Nice to learn!

[anvil-on-my-toe]

I've definitely noticed it on meat that has gone off, and previously was not iridescent. I wonder if bacteria create surface gratings.

[TheBlight]

Maybe the effect can manifest when oils from the meat/fat and water separate similar to the effect with gas/oil? With this hypothesis the iridescence would be incidental to the meat having gone bad but more to do with age and not maintaining structural integrity/consistency.