When opening the simulation or at Reset at the chart of the Julia set you see the unit circle surrounded inside and outside by circular blue shaded areas.
The green rim of the unit circle is the Julia set of the white point c = (0,0) in the plane of the Mandelbrot chart. Color shading indicates how fast points outside diverge and points inside converge to zero. The criterion of inside shading can be adjusted with the slider (higher value for less differentiation).
For all points c the Julia set is the green rim of the fractal. Blue areas are those of fast, red those of slow divergence or convergence to zero, and do not belong to the set. The slider varies the gradation of shading. This gives additional insight into the convergence landscape and increases the aesthetic beauty of the fractal structures. Shift the slider at high resolution!
Most impressive large scale structures are calculated for points at the rim or outside of the Mandelbrot fractal. Yet at high resolution the apparently simple structure for points inside reveals interesting fine structure, recalling that of coastal lines or of natural surfaces.