I haven't had any down leakage to speak of, so not sure what to say there, have you asked Tim directly? He's "the man" when it comes to quilts IMHO. I have Black/Charcoal 10d combo as well, so not sure why you'd be having down escape. Whether the black is inside or out, it's still very light fabric, so I don't think it will be that noticeable vs. the charcoal.
Considering how thin the 10d is it's not entirely surprising that there could be leakage, that's one of the compromises with gear like this. Although I can imagine it's disheartening to find down outside the quilt, you'll likely never lose enough to actually make a difference. A couple feathers may seem like a lot emotionally, but rationally this stuff is so light it'll take years of minor leakage to add up to anything noticeable.
For my overfill I asked Tim to put in what he thought was needed, it went from 13.4 to 15.1 and seems just about perfect. That overfill made a huge difference in keeping the down more evenly distributed, on my core. I hated to add weight as it was so light, but glad I did now.