That’s cause it doesn’t have any lights attached 
These days you have to set a rootNode.setLightCombineMode(LightState.OFF); for “default” colors to show up. I’ve fixed this in CVS (well in 2 seconds anyway done). Thanks for spotting it!
Someone actually added an alternative method to the wiki; lightState.setEnabled(false). You also no longer need to detach the existing lights (for either method).
Thx for the fix and info llama, getting it now… I love CVS…
[EDIT]
Hmm, still broken. However, now that you've given me a direction to look in, I'll see if I can solve the problem… 
[EDIT] Fixed!