Vertex Color Layer = named Col?

Using Cycles.
Used Vertex paint to create a mask
created an Input>Attribute node
typed ‘Col’
plugged output Color into Factor of a Mix Shader

My question is…how do you determine the name of what to type in? The only reason I know ‘Col’ was the name of the first layer was from a really old thread here.

Perhaps I should just post on that thread and revive it? My apologies if I shouldn’t have started a new thread.