Second test using two Polarizers, circular and linear, to work as a variable ND filter. This time turning auto exposure and AWB on. Then I locked the camera to wide open (F1.8-2.4, depending on focal length). Finally, I white balanced the color shift. Did it in the shade of the tree which warmed a bit too much (to some) -- it's like balancing to a blue colored card.
Photos of setup are down on the right of this page.