I'm in 2 different portrait classes. The 2 paintings on the left were done in a single session, the one on the right was done over 4 weeks (using a different color palette, too).
Andrew Lattimore's class (WCC) is based on a 5 week pose. Plenty of time to work things out (or, in my case, maybe too much time!) Andrew stresses value and proportion also; when teaching color, his approach is more experiential.
Hopefully, all this experience will kick in over time. The oil painting gods will smile, my paintings will become fresher, bolder and more beautiful ... painting nirvana:)