Vertex Colour with grunge opacity texture on top?

[lewis.brooksKTBH7]

Hi, i'm trying to assign a model with a vertex colour for the base but also stack a grunge layer on top of it as a part of 1 material, the grunge map comprises of a diffuse and opacity map whereby I need the vertex colour to show through where the opacity map does not cover. How can I go about this, OSL Composite?

[CiroCardoso3v]

Any example or screenshot of what you are trying to accomplish?