I'm not sure all this belongs in the main docstring.  Seems more like something that should go in a regular comment.

The doc string should probably just say something like "This class also serves as the base class for chromatic subclasses, including Chromatic, ChromaticAtmosphere, ChromaticSum and ChromaticConvolution.  The basic functions that all ChromaticObjects can do is to draw themselves when observed in a particular bandpass and to evaluate themselves at a particular wavelength with evaluateAtWavelength.  See the doc strings for the draw and evaluateAtWavelength methods for more details."  

Then users will know where to look for more information.  But I don't think they need all the gory details about what they need to define if they want to build a subclass.  I think that belongs in a regular comment that a developer will see when they look at the code in detail.