Black ceiling

Hi guys, i think it is pretty basic stuff but I can´t figure out how to make my ceiling white in Rhino render it always turn out black.
Does anybody know?

either you set the material to layer or you have some double sided material, or its set to shaded when the layer color itself is black with setobjectdisplaymode, there are several options. if you post that surface (export selected for instance) then one could have a look.