bug#8049: 24.0.50; doc of `list-colors-sort'

[Drew Adams]

> > The doc should explain what is meant by RGB and HSV color 
> > distance here.  There is not only one possible definition
> > of color distance, and many users will not
> > have a feel for this or prior knowledge about it.
> >
> > There is nothing in either Emacs manual about this, so the 
> > doc string needs to cover it.
> 
> There is no detailed explanation in color.el either,
> so I don't see a need to do this in `list-colors-sort'.

Huh? Whether the source code explains something users need to know is beside the
point. Users are not expected to study the source code (although they are
welcome to).

This is about a _user option_, not about the source code.  And no one said
anything about a "detailed" explanation.

We give users a choice of behaviors, but we do nothing more than name two of the
choices - no real description to let them know what is involved, what to expect,
how those choices differ from the others.  Users deserve better.