Color scheme changes.

Colormap on the 2D plot changes to gray when the model centroids are overplotted
(for visibility) but gets back to gist_heat when the model isn't overplotted
because that looks nicer (And I still wish there was a grayish but not
completely gray colormap, as it is a bit... gray right now.)

This also marks the end of the  "major things" to be messed with - turned out
not to be so major after all.

Next: write good docstrings.
Small corrections, added screenshot folder.