OP is talking about the Gouraud shading(I think that is what it's called) that OpenGL exhibits when viewing objects/faces obliquely, especially in an un-textured or colored model. In essence, he wants a primitive emitter in Sketchup.
Or--that's what I get from one reading
EDIT: if emitter is not the correct term, then the ability to selectively apply or not, the OpenGL native shader.