How to get the specified material for a given uv coordinate

I have two materials attached to a object and I am trying to create a texture2D based on the materials. To do that I am trying to determine which material is applied to what coordinate. I tried to use Mesh.GetColors() to get the list of colors listed by indices and try match that to vertex and back to uvs. When I do this I get no colors back and I am guessing it is because the mesh itself does not have colors but is simply having a materials colors applied to it. Any help would be much appreciated.