How can I bake mesh colours so they appear when rendered in Vray?

Modelab tools does this well. Unfortunately, I don't want my colours to bake on several geometries, but rather a smooth gradient throughout an object.

So I converted to colouring meshs. Once they're baked, I can view them in Rhino using the rendered viewport. Though once I try to render them in vray, they remain white.

I'm quite incompetent with other renderers and would be good if anyone knows the answer to my query or drop some hints to point me in the right direction!