Too many materials and draw calls? Unity/SketchUp

We are developing a game for mobile phones. All the model making is done in SketchUp.

Although the number of materials/colors applied to the models within SketchUp is low, Unity reads unreasonable numbers of materials (judging same colors/materials as different many times). Therefore, too many draw calls are being generated, causing performance drops in dense parts of the game's scenery. Any suggestions on fixing this problem? Thanks!