Setting "Material ID" For Use With LPE

IceCrMn

I would like to set a "Material ID" for different surfaces for use with LPE.

Do I set the material ID in the shader pane?

For example...

I select the skin surfaces I want my LPE to effect and assign them RGB 1 1 1 on the color selector named "Material ID".

I want to use the LPE

C[<L.>[1 1 1]][R]{0,3}[S]{0,3}[T][R]{0,3} | C[<L.>R][R]{0,3}[S]{0,3}[1 1 1][R]{0,3}[T][R]{0,3}

Do I have the Materials ID correct in my LPE?

Does LPE use RGB shadre Material ID?

Do I use the "Tags" instead?