Visualize # of dependents?

I'd be very interested to see a visualization that reflects either the number of direct dependents or the total dependents in a graph rooted on each package. It might use brightness and/or color. Size probably doesn't work that well because size is so influenced by distance.

No files, tests, or entry points are named. Start by locating the existing package graph visualization code and determine how direct and total dependents are represented; done would be a visualization that communicates one of those counts using brightness or color without relying on node size.

Written by the indexing model from the issue text.