Hi Dirk,
I haven't seen any animal that looked like something in between. From what I have seen on Okinawa island, I would say that both forms seem to live isolated from each other. Also the habitats in the north are completely different to the habitats in the south. The northern form of G. kuroiwae lives in huge montane rainforest, and we found them on rocks along small rivers and streams in very wet areas. The habitat of the southern form consists of huge karsty limestone rocks with tons of little caves and crevices (see the pic in the post of the southern form ). There were no rivers and we found them at the cave entrances or on the ground in less wet areas.
We also searched for G. kuroiwae in the mid part of the island, but couldn't find any. That does not mean that they don't live there, but as I also have never heard of any kuroiwae findings from that area, it would be worth to think that today, both colour forms live isolated from each other and do not mix up.
Cheers
Thomas