Hi Rich, look for things like "false color" or "vertex colors" something like this:
http://geometrygym.blogspot.com/2011/09/mesh-false-color.html

You want something that will let you specify colors per _vertex_ rather than a per _face_ color value.

Most mechanisms that allow you to supply color information at the per-vertex level will also handle interpolating the colors along the interior of the polygons that connect the vertices.

- Michael