A couple of days have passed. From this pic you can see that I'm masking each block to keep the lines clear and sharp and exercising care by allowing 24 hours drying time before I mask and paint the remaining alternate white areas; otherwise the painters tape might lift the fresh paint.
This side of the neck is shaded. Note the intensity of color...
...and that the hue perfectly matches the painters tape.
(If I'd used green tape it would have been easier to line up along an already painted line. Ain't hindsight grand?)
Perfect uniformity is not something I labor over. Variance humanizes art. However, there is a happy medium between rigidity and chaos. If something jumps out and my eye returns to it over and over again, I make adjustments until the feature disappears into the whole. At the end of the day I stand back and look for just such glaring differences. There are a few on this side of the neck which will need touching up.
I'll be adding highlights to the facial areas later.