I created a prop - a control panel with many different parts mostly made from primitive shapes. The final piece looks good with all materials attached. When I export as a prop and then import back in - the materials I assigned are gone?!? 

I know I've seen certain props with various material assignments.  How do you create the material assignments?

Let's say you have a red ball and blue cylinder.  If you save these as an OBJ they come back with just a PREVIEW color for both. I want to keep the separate materials of each shape.  I don't find the grouping tool to intuitive - I've made some headway but the groups I'm assigning get lost when I export as a an OBJ. Is there some check box I need to use to get all the existing parts saved as a group of objects?  I've downloaded OBJs from the interent and have seen where different areas of the props are assigned different mats thus giving the user user the ablity to color it to their choosing.   I can't figure out how to do this....please help and thanks

Windows 10 - Poser Pro 2012 - 64Bit - 24GB RAM - 4 x 3.40 GHZ processor