Editor icon and thumbnail colors - What do they all mean?

I’ve been trying to find information that explains what the various icons and their colors mean when working inside the editor but can’t find anything. The documentation is massive and trying to find something like this is not easy and I’m not even sure it is documented (I imagine it probably is - somewhere). Even the beginner videos don’t seem to explain this - perhaps it’s not important, but it’s driving me crazy for some reason.

Does anyone know where I might find this documented? I’m sure they’re colored for a reason - I’d like to know what that is.