Is it a dark scenery? That could explain your problem.
If you want to colour it accurately, I'd suggest using a white or very light coloured scenery. If the scenery is a darker colour to begin with, it will turn out a much darker colour than you have selected on your Palette. Dark sceneries are impossible to make lighter by colouring them in Polyworks, but light sceneries can go pretty much any colour you want them to be. Same as textures, thats why I prefer textures that are light grays or whites (unless I'm multitexturing)