render issue / mesh colors

Hi all,

I noticed that when you color a mesh in rhino (with vertex color data, not with texture), once you pass into render mode, the object loses its shadow aspect.
On this image you can see the same mesh, one without color and one with, both in the same rhino viewport.
I cannot find where I need to change the settings in order to also have this shadow aspect on the colored mesh.

Thanks in advance,

Roger