Superformula
Gielis's superformula: a stack of shapes morphing, shrinking and twisting inward.
Pens
Nested shapes form color bands. A single shape changes color around its outline. Starts with 3 pens and works with anywhere from 1 to 8.
Settings
Symmetry m, n1, n2, n3, Shapes, Inner scale, Twist per step°, Morph ease, Smoothness.
The preview uses the default settings on A4. Press R in the app for random variations. The SVG export is in millimetres with one Inkscape layer per pen, so it works with the AxiDraw extension, vpype and saxi.