I tried the new removal of colours from a range selected using the paint brush. When i press the alt key a pair of scissors appears, with no cross hair, so I have no idea what the select point is. As I click around or drag around inside the existing mask, nothing is altered.
I think you might be misundestanding how the new colour removal option works Adrian. Pressing the Alt key changes the cursor to the scissors, then you can click on an existing colour marker (eyedropper) to remove it. Unlike the eyedropper, which you click on the image to add a colour to the mask, the scissors only remove an already added colour selection.