Last edited by xpatUSA; 7th August 2019 at 11:30 PM.
Ted - this is the outcome from a discussion Richard and I were having on another thread which dealt with how to get a decent WB if one does not have a gray card along in a studio shoot that uses a neutral seamless background:
A few from a shoot with Celyne Moh...
You are making your assumptions based on the posted image, but not the original Richard was working from.
In my experience when shooting on white seamless paper, the model is usually 6 - 12 ft (2 - 3.5m) in front of the paper. The light is set so that the model is properly exposed, so there is a reasonable amount of light drop off (inverse square law) when it reaches the paper. If the paper is "white" we are effectively shooting a huge gray card and can usually pull a decent white balance off it.
The only exception to this rule is when the photographer lights the seamless backdrop on purpose to ensure it is pure white. The subject is lit to a level between 1 - 2 stops below the light on the backdrop. This technique is used in alpha channel masking to extract the subject from the background and placed on a different background. It can also be used when the photographer wants a pure white background in the image. In this case, pulling a white balance off the background is a bit more tricky, but not impossible. Background paper is usually used as the place where the model is standing (as in Richard's shot). One can usually find an area that is gray enough to pull a decent WB.
I didn't have an option of what to click on since I did not bring my WB card. I normally will use the WhiBal card which provides very close balance when clicking on it.
Actually, this shot, done in Auto White Balance was closer to correct (pleasing) WB, SOOC than on Sunday when I used the camera's flash white balance.
So long as the background is neutral, in my experience it makes no difference. I've pulled decent white balance off black, white and gray seamless paper.
No doubt a proper neutral gray target positioned near the model's face would be the best solution, if it is available. If not, the photographer has to make do.