This formula allows you to shade areas within the foreground colour picked using your brush. Very fast shading as you don’t need to do any masking. I call it:
- “Shade select fg colour only”
-Here is the formula for left button - if( a==fg, a+1, a)
-Here is the formula for right button - if( a==fg, a-1, a)
Here is an example gif to explain what I mean visually.