Vertex colors behaved differently as the paint overlay mixed the colors in display mode and the results was multiplied on top of the original shading. This patch will align the implementation to texture painting where the colors are drawn by the workbench engine so the correct shading is applied. This also means that we don't show the vertex colors overlay when not in solid mode. Reviewed By: fclem Differential Revision: https://developer.blender.org/D6436