It's not like when the player enters a cave, the illumination model breaks. The white floor isn't the reason TTC looks is consistent. The lighting looks great when running around a red cave. Better, even, because of the translucency of the materials along with the dynamic, localised light sources, although the game lacks hard, dynamic shadows. That is, the lighting model isn't predicated on having a bland, open, white environment to work well that fails when the environment changes. Heck, it
can't be because the game has a dynamic day/night cycle!