Hmm, I see–you’re quite right, the model does have materials, and is rendered white when no light is set. My mistake!
Looking around the forum a bit, I found this post, which may explain it, presuming that this behaviour hasn’t been modified since then.
In that case, try changing your material such that the colour is stored in the “ambient” colour, rather than the “diffuse” colour, and applying an ambient light–that might work.
As to transparency with vertex-colours, it can, technically, be done. Panda’s vertex-colours have an alpha channel, but Blender doesn’t have a means of setting the alpha-value of a vertex-colour, and I believe that YABEE doesn’t export it. However, one can modify YABEE to use a second layer of vertex-colours as a source for the alpha-channel of the vertex-colours. But this might be overkill in your case!
Depending on the specifics of your project, a simpler solution for this object (presuming that you don’t apply an ambient colour, as I suggest above, or that doing so doesn’t work) might be to just apply an alpha-scale in code, like this:
myObject.setAlphaScale(someAlphaValue)