My beardies have developed black spots over time as well. From the picture it looks like it is located only on the one scale. If it is not spreading to the other scales, there is no degeneration or sinking of the the skin around that area, and otherwise the dragon is fine it is probably just like a freckle or mole that we can also develop over time. Once my dragons have developed their black spots they do not seem to go away even in shed, and they are perfectly fine.