White southern pine is good for thermal mass—the waxes act like a eutectic salt. But it would need insulation on the outside, and suddenly it's a white box again.
Compare
Hütte Hut™:
http://tinyhousetalk.com/dome-inspired-teardrop-camper-hutte-hut/
Lower frontal area, and it not so dark and oppressive inside. It has pretty refined construction. The white part is an aluminum frame. And the wood ribs are little bow trusses.