Press green flag. Set the sliders "r" and "InToOut". There are 3 backgrounds. Press b to change between them. PRESS ONE OF THE NUMBERS 1 - 9 to see a pattern. When the pattern is finished, press c to see the inversion circle. Sorry, the code is somewhat clumsy. If you want to remix using other expressions, you must make the change in two places, see comments in sprite nr1 and nr2. (And I sincerely hope that I got the inversion correct. If not, please, let me know!)
I combined the idea of using an expression for coloring the scene point by point with the idea of inversion in a circle. Only the inside (InToOut=1) or outside (InToOut=0) of a circle with radius r is colored using the chosen expression. Each point on the other side has the same color as its inverse. Lots of thanks to Leszpio and Scratch-Minion!
