objects only appear as black silhouettes

Hi,
I'm just trying to run the following simple bouncing ball example from the
vpython site:

*from visual import **

*floor = box (pos=(0,0,0), length=4, height=0.5, width=4, color=color.blue)*
*ball = sphere (pos=(0,4,0), radius=1, color=color.red)*
*ball.velocity = vector(0,-1,0)*
*dt = 0.01*

*while 1:*
*    rate (100)*
*    ball.pos = ball.pos + ball.velocity*dt*
*    if ball.y < ball.radius:*
*        ball.velocity.y = abs(ball.velocity.y*)
*    else:*
*        ball.velocity.y = ball.velocity.y - 9.8*dt*


It runs without errors, but the floor and ball objects are black, without
any visible surface detail.  The silhouettes of the objects are visible if I
change the background colour to something other than black, but changes to
the colour of the objects don't affect anything.  I'm running this on a
fresh install of Ubuntu 10.04, python 2.6.6, and it says I have version
1:5.12-1.1 of vpython.

Any help would be appreciated,
Thanks,
Vijay

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