My pencil (and brush) is set to white and painting it over white yields grey.
Mode is normal and opacity is 100%.
The Layer is Normal and opacity is 100%.
Obviously, I accidentally triggered something and there is no obvious-to-me way of going back.
I've tried resetting the paint brush and pencil tools several different ways, but the behavior is the same.
Painting on my mask yields grey. I can paint black just fine. Just not white.
Photoshop decided E6-E6-E6 was white enough for me. Dunno what magic Ps used to decide to do that, but THANK YOU!!