After editing 'stamp' also known as brush shape or head, make a selection, at the bottom (depending on your layout) selection options, tap 'brush' to add as a brush. In brush settings under the 'head' section activate invert and color buttons.
I made this with my finger on my phone because I forgot a stylus. Ignore the sloppy 'trimming'. It is purely to illustrate that it can be done on mobile.
(Thumbnail from YouTube video)
Uncomfortable(from description): "Some people come out of the womb swinging, brave and ready to take on the world. The rest of us... we're a little more timid, held back by fear and anxiety. In this video, I talk about how I spent many of my younger years terrified and intimidated by the idea of a blank page, and how I ultimately worked to overcome it."
