I am running Ps CC 2014 in my iMac. Since I got the latest update a few days ago, I am not being able to paint on a white mask with black or any shade of grey. For example, I added a white Hue/Saturation mask to my image and wanted to paint certain areas in black or grey, but nothing happens when I brush the mask. The history panel shows that I've used a brush, but there is no effect showing on the mask. If I invert the mask to black, then I can paint it with white or shades of grey, and this is with any kind of layer mask. Perhaps I changed some setting by accident? I only recall changing some settings for my Wacom, not Photoshop. Any input available? Many thanks!