Point elements in GPL can be color as color.interior or color.exterior. A number of clients that I have worked with prefer to have a solid dot on a scatter plot, but without the black circle around it. This might seem minor, but it looks a bit softer, and afterall if you want it, you should be able to have it in GPL. This example seems a bit crowded, and might be better with the open circles, but illustrates the grammar nicely.

To my mind, the grammar should simply be color if you want both to be the same color. As in color(sex). If you do this it behaves like color.interior(sex), color.exterior(color.black). Why?? You've got me, but I am pleased to report that in 16.0.1 the code in the .pdf works just fine. Recent experience in 15.0 was producing errors. So the result might be a little verbose, but works just great. Hoorah! color interior exterior.pdf