Really, not much, I'm not that original. Some WIP handwave will have the two species be related somehow.

Mataluno range from a periwinkle to indigo (this is off of memory, I believe I changed it, I can give you the exact colors later). This is much like the melanin in humans. Mataluno also have breathing flaps (essentially land hills) on their neck. Mataluno legs are also jointed differently, letting them (in theory) relax on their backwards-bending joints.

I think with the Mataluno my method to distinguish them will be through culture.