It needs to establish some way to say that this segment is the "base" layer, this is 1, this is 2, &c., but it has some potential, and it's worth a think now that I've gotten 80% of the way toward being able to draw notation in color n.
Draw notes from the "base" segment in black, the "layer 1" segment in green or something, and so on. Or even just "active segment" and "not active segment" would be helpful. Vary the opacity or something. Out of scope for Thorn, but not out of reach for just beyond, and worth a serious think.