I can finally confirm that I have the actual "dark form" of Tinantia pringlei - very rare in Europe where the light form is the only type in cultivation.
These pictures are of plants grown side by side in identical lighting, so you can see the difference. They both have purple spots, but the base green colour of the leaves is really different between the two. Supposedly there's also a difference in flower colour but I don't see it 🧐