G3dviewer adds team color to some of tree models. For example tane.g3d from autumn tileset:
It also happens with models from other tilesets from megapack ( for example new desert4 tileset adds color to palms too.)
While as I was informed this is not a bug but the models are faulty I think many moders will probably not be bothered by it to fix them, because those models look ok in game, and not many people view them in the viewer anyway. If it would be a trivial thing to implement then I propose to add a "No team color" option/mode to g3dviewer that would allow to view those faulty models.
If it isn't trivial to implement then maybe it is not worth it though.