Maya - Vertex Colors and Blendshapes

Hey Polycount!

Sorry if my first post in a long while is a question but Maya has driven me into a corner!

I'm in need of a blendshape driven vertex colour system that will colour my polygon's vertex colours as they are displaced from their original position.

What I'm thinking of at the moment is calling the current vertex positions of a polygon into the node editor, followed by subtracting the original vertex position of the polygon. I would then turn any vertex with a non-zero value into "1" and assign it a vertex color.

My questions however is:
-Is it possible to call displaced vertices in Maya and use them in an expression?
-Is it possible to call vertex positions at all?

I've attached a screen of what I hope to achieve below.

Thanks!
bluerebel