As I already mentioned the white balance is something complex, often subjective and mostly wrong!
A few years ago, I made a summary that was translated into English
The only thing that is pretty much right is the matrix operation between the illuminant and the base color found on the spectrometer.
But in the majority of cases, the problem is that we do not know the iluminant - if we knew it, the problem would be almost solved, nor the spectral color of the subject (flower, face, sky, etc.).
We are faced with a problem where there are more unknowns than equations
The alternative solutions presented in eg Photoshop or other software like Ufraw (patch for skin), are only work around and do not solve the problem.
But they give the impression of doing something serious, omitting a parameter from the equation
I do not neglect these solutions but in most cases they are false.
Creating a target gray mask (or other hue) is a solution to target / reach a color, but is generaly obsolete for the white balance.
Indeed the gray that we will target on the image itself depends on the coefficients of the white balance that is applied to the red, blue and green channels.
So in French “c’est le chat qui se mord la queue”; it’s the cat that is biting its tail.
It is the same if one uses the skin, whose variation of hue is close to 1 radian, which is enormous.
As I said the real solution is to take the picture, as would Alfred Hitchkock who always appeared in his films, putting a gray chart incorporated into the scene.