I have found a bug found in Lightroom 6. When I use the adjustment brush, I use the ‘show selected mask overlay’ feature but with Lightroom 6 it is hardly visible when you make an adjustment. Very very pale pink. With Lightroom 5 it was much more visible. If I go to adjust an existing photo I altered first in Lightoom 5 and open it in Lightroom 6 the mask overlay is much deeper pink but as soon as I brush on more adjustment, what ever I add shows as pale pink. The problem happens when I use a Wacom tablet or Wacom mouse. I have just had a chat to Victoria Bampton and she just reproduced the same problem with her Wacom tablet. With her Apple trackpad though it worked fine. I am using Yosemite 10.10.3.