Ok, you guys are all going to laugh at me, but in service to the community, I kicked this up to a friend whose job is to calibrate colors for a major print company for technical analysis. This is what I got:
“So the left Lab is before I grey balanced the background of the portrait, and the values to the right are after grey balance. L is luminance, so brightness where 100 is the brightest white. A is the green to red axis, where negative a is green, and positive a is red. B is the blue to yellow axis, negative b is blue, positive b is yellow. So the grey balance brings the a and b both closer to 0 (true neutral), though the b value is affected more, reducing the yellow amount.
But basically as the b value is not negative in either version, it’s not blue”
