Workshop · Night 8
Paint on the canvas. Black hides the top layer, white brings it back, gray goes halfway. Watch the mask thumbnail in the panel on the right change as you paint, because that thumbnail is the part everybody misreads.
Two thumbnails, one layer. The left one is the picture. The right one is the mask. Clicking the wrong one is how people end up painting on their photo.
A mask thumbnail that is solid white means nothing is hidden. Solid black means the whole layer is gone and you will swear the layer deleted itself. If your layer vanished, look at the mask before you panic.
Press D to reset to black and white, then X to swap them. Hide, reveal, hide, reveal, without ever leaving the canvas or opening the color picker.
The Eraser does the same thing to your eyes and something completely different to your file. Flip the mode, scrub a hole, then try Bring it all back. That difference is an exam objective.
Masks are not on and off. 50% gray gives you a half-transparent layer. That is how a gradient on a mask fades one photo into another without a single eraser stroke.