Sometimes you can catch the sapwood layer above the heartwood in transition so that it takes some of the heartwood color.
The sapwood layer above the heartwood turns to heartwood in a living tree.
There are exceptions but the best scenario is a heartwood back.
I've made lots of BL bows and the heartwood is clearly delineated from the sapwood.
However, I've always felt (can't prove it) that Northern BL is better and tougher than Southern BL with fewer inciidences of chrysalling. At least, for me. and from what I've heard on here. I have not had that many bows of BL that have chrysalis that I can remember and I learned on BL. But it's been awhile since my bow beginnings and I'v never taken notes.
Now, white ash on the other hand almost always chrysalled for me but bowyer friends from around here have been pleased with it.
Jawge