This is an implementation of the domain coloring technique for complex polynomials visualization.
In this technique, the value of a polynomial at point (x, y) is colored according to some rules. You can see where each point is mapped, in this implementation, by comparing the image on the left with the following reference image:
The selected domain applies to both graphs. By selecting a larger domain, we can see clearly that the lightness increases away from the origin.
You are encouraged to draw your own polynomials to visualize how they transform the plane. One nice thing to do is to observe the polynomial's roots, which always have a black spot in their neighborhood. You can also notice how double roots are different from single roots and how counting the roots with their multiplicity always sums up to the polynomial's degree, exctly as told us by the Fundamental Theorem of Algebra.