You get a different look when you start alternating black (000000) and white (FFFFFF) in Scribbler Too–sort of fuzzy marbling. The lines get quite spiky, so you might want to dial down your radius somewhere around 15-20, or even less if you want actual detail.
I do most of my black first with the radius set around 30, dialing down to 7-10 for eyes or other detail. Then I switch to white and sort of blast the color around. In other words, instead of drawing steady lines, I center the pointer where I want the most white to be, and tap the mouse button. The I move to another spot, tap and keep doing this until I’m happy.
If I get too much white, I switch to black and do the tap, move process again. I may switch back and forth several times, adjusting my radius as I feel it is needed.
To get rid of solid lines around the edges, I set the color to white, move the mouse a little way from the edge and tap. I move the mouse all along the outside tapping whereever I want a less solid line.