This is what I would do:
1 - In Sketchup
Give temporary colours to the various parts of your model, e.g. if it's a kitchen cabinet give different colours or textures to the base cabinet, the doors, the handle(s), the work top, etc.
Then export your model as a DAE file
2 - In the Library Editor
Import your new model; delete your old model, save the file
3 - In SH3D
Import the library
Now insert your model in your design.
Do Modify furniture -> Materials -> Modify. You will now see a list with the different parts of your model. Click on a part and assign a new colour/texture.

H