solid black over glowing (emissive) effect

We have a sphere with some special color effects, and a glow effect (high emissive color), with on top of that a mesh of a questionmark. The questionmark is supposed to be solid black, so it is clearly visible, but the glow effects seems to effect the blackness of the material of the questionmark. Is it possible to tell the engine to render the questionmark solid black, without being brightened by glow effects of objects behind it?