I would like to reproduce the curves as shown in the picture below (taken from here):
I don't know if this was produced via LaTeX, but possibly TikZ or something similar was used. I guess that a "foreach" loop could have been used, which would also allow to change the color automatically. But how to reproduce this brush-painting style?
The curves look like elliptic curves, with equations of the form
$y^2 + a_1 xy + a_3 y = x^3 + a_2 x^2 + a_4 x + a_6$ with the $a_i$ being real numbers.
Would you have any hints/ideas?

