Sounds like it's the doe that carries the otter <at>.I just examined the Doe quickly & here are the quick notes. I will take pictures later today when I take pictures of kits. Doe has a greyish belly definitely not a Black belly like the Buck. She also has light brown/tan markings on her ears, especially the edges. Now I doubt she is a self Black.
I've never had a seal otter but it sounds like you may.