difference between cave and Inspector

[VizMars]

Hello,

I am using the vizcave module to present objects stereoscopically. When I add my 3d-model (chessboard.OSGB) to the world it looks much brighter than the model I created. In the Inspector, however, it is displayed as expected.
Turning of the ambient light doesn't seem to fix the problem.
Why is that?

Please find attached the code, the screenshots and the model.

import viz
import vizcave

CAVE_WIDTH = 0.59773
CAVE_HEIGHT = 0.33622
DISTANCE = 0.70 


viz.setMultiSample(8)
viz.go(viz.FULLSCREEN)	
viz.clearcolor(0, 0, 0) 

PowerWall = vizcave.Wall( upperLeft=[-CAVE_WIDTH/2.0, CAVE_HEIGHT/2.0, 0], 
				     upperRight=[CAVE_WIDTH/2.0, CAVE_HEIGHT/2.0, 0], 
				     lowerLeft=[-CAVE_WIDTH/2.0, -CAVE_HEIGHT/2.0, 0], 
				     lowerRight=[CAVE_WIDTH/2.0, -CAVE_HEIGHT/2.0, 0] )
							
cave = vizcave.Cave()
cave.addWall(PowerWall)
# creates a dummy-tracker (a group object is an empty node)
head_tracker = viz.addGroup( pos=[0, 0, -DISTANCE] ) 
cave.setTracker(head_tracker)
vizcave.CaveView(head_tracker)

board = viz.add('chessboard.OSGB')