Colouring related surfaces differently

[murphsan]

Hello all,
I've modelled (Wildfire 2.0) a housing casting that requires several tooling (mould) directions.
I'd like to cosmetically colour the surfaces differently which belong to each separate tool.
However, when I pick a surface it picks the entire surface originating from it's geometry creation, and they cross over my tool split lines.
How do I just select discrete surfaces ?

Thanks for any help.