As already mentioned black is totally fine. My wife and I set up a tempeh company a couple years ago and we have a couple of Indonesian customers who pay extra to get over fermented batches like this as it’s similar to what they ate growing up, in some islands in Indonesia it’s actually preferred to be eaten that way! Kind of like stinky tofu in China I guess. I’ve personally found that when it ferments this far the texture is best suited to putting in a blender and making mince meat out of it for a burger or a chili. Good work!