Really like the idea of a two-tone contrast that stays within the current OSB aesthetic, but pushes it in new directions. I think that would be something that is subtle yet stand outs, and classically trad but boldly innovative. That said, not sure exactly what "that" would be.
Natural CXL seems like a challenging color to use in a two tone contrast. It is a bit of an enigmatic tone in the first place, and even slight variations at Horween seem to quite dramatically affect its appearance.
The loden/natural or navy/natural could be interesting, but they would definitely be very high contrast.
I'll just add another idea into the ring. I think something with reddish tones could go well with natural. Here are pics of the cherry and natural trail oxfords. Cherry may not be the perfect reddish tone to pair with natural (and I don't know if George has any cherry in stock), but I think it suggests that a natural/reddish-brown pairing could be interesting. (An intrepid photo-shop wizard may be able to give a more definitive answer.). My suggestion would be to have the cherry on the "collar" and lace portion and the natural on the lower piece (as in the two tone boat shoe George posted above. However, the backstop could also be left natural, methinks, so as to avoid confusion with a bowling shoe).


Other ideas for a two tone, besides a color contrast, would be a contrast between textures, such as smooth/pebble or smooth/rough-out.