Thank you... ...did not realize the needed use of the Mask Tool's "Set Mask" buttons to achieve a 0 to 100% Gray tone mask for the Saturation transform.
.
Set Mask.jpg (37.63 KiB) Viewed 743 times
.
I agree that if all masks start out 0% Black that perhaps this might save some confusion/forgetfulness [at least for me] but where an initial all 50% Gray mask has some nuance possibilities, how about adding a 50% Gray to the "Set Mask" buttons?