I was reading something the other night about using the gradient tool with the mode set to difference so I started to play around with it. What I did was:
1. Created a new image with file/new 20cm & 14cm 300 resolution.
2. Chose blue from the gradient set simple and set the mode to difference.
3. Started with linear and then reflected gradient and used quite a few long and short strokes going in different direction.
4. Added a bit of radial and diamond gradient , using quite short strokes, to give it interest.
5. When a large area ...