Creating 3D PDF Files

Hello, I need help displaying 3D models in Acrobat 3D PDF with color. 
The models with solid colors always appear grey in Acrobat 3D PDF.

1. I import my 3D model into Photoshop as .OBJ. The model looks correct with all the solid colors.  
2. Next I export the 3D model as 3D PDF.
3. I open the 3D PDF file in Acrobat and the model is all grey without any solid colors that previously appeared in Photohsop. 

Not sure why the colors are not appearing in Acrobat 3D. Is it an issue from Photoshop or Acrobat?
Any help would be greatly appcreciated.