GeezerVison

I think you can be more straightforward. ColorizingArtist is the base class for everything that "can be colormapped". Directly instruct to create the base class and pass it to colorbar. This the detour "typically subclasses with data, like image, but you can create without data" is not needed for the context of creating a standalone colorbar.

Thank you for the feedback, does the following read more easily:

"""
A `~.Figure.colorbar` requires a `matplotlib.colorizer.ColorizingArtist` which
contains a `matplotlib.colorizer.Colorizer` that holds the data-to-color pipeline
(norm and colormap). To create a colorbar without an attached plot one can 
use a `.ColorizingArtist` with no associated data.
"""

(and should we remove the last sentence?)

This is okish. Maybe an improvement would be to switch the last sentence for

To create a colorbar without an attached plot one can directly instantiate the
base class .ColorizingArtist, which has no associated data.

Done :)