I have a tree which I created in tree[d] and I converted from .x to .egg
When you view the model in pview or in my own game it looks fine without the lights on, however when you turn lighting on the leaves become dull and lose their color.
I am guessing it has something to do with the interaction between vertex, polygon and material color.
When you enable lighting on an object, it uses the material color. Your material color specifies white for diffuse and specular. The diffuse color is what you normally see as the dominant color of the object, so the diffuse color of white is why your object has no color when you enable lighting. If your material didn’t specify a diffuse color, it would use the vertex color for the diffuse color, which is the color you see when you don’t have lighting enabled.
Short answer: edit the egg file and remove the diffr, diffg, diffb specifications from your material, or remove the material (and the MRef’s) altogether.