In older versions of Poser (versions 4-6) I noticed that there is a texture for the ground plane (Ground Default Texture.tif).  I seem to recall that it shows up as brown in Poser.  I think it also renders, but I'm not sure.  In Poser 5 and 6 it's located in the main Texture folder.

You could use this file to make it any texture you want using Photoshop, Paint Shop Pro, or any other photo-editing software.

Forgot to add:  You can not apply a material to a prop/figure that the Mat file is not intended for.  You will get strange results.

Also, as was mentioned, if you want to combine scenes, the File, Import method is probably the best.  I had found that if I only want to bring in a few props or characters into a scene, I just save them temporarily in my Figure or Props library for that purpose.  An entire scene would be better using the File, Import method.

Poser 2, 3, 4, 5, 6, 7, 8, 9, 10, Pro 2014, 11, 11 Pro