I am sure this is not a matplotlib problem, but I am not sure whos it
is, so I'll start here:
the blue and green dots should only be inside the circle.
Run the code, you get a window that has a 'save' button, the dialog
has a 'type svg' option
the svg renders with the blue/green dots everywhere (rendering using
both rsvg-view and inkscape, which use different rendering engines.)
save as png, display png, dots only inside circle.