The weft is totally going to be black.
I have 1,800 yards of black fingering in my stash. With fingering, instead of lace weight, it will take about 2,600 yards, so I need just a handful more skeins.
The stripes will be at the bottom of the poncho and there will be about 8 inches of black at the top. So, I need another 184 warp threads of black.
If I do not have enough tencel, I will add it to my order of black fingering...
Now, to finish those baby blankets!