Display names of defined colors, and show what they look like.
If the optional argument LIST is non-nil, it should be a list of
colors to display. Otherwise, this command computes a list of
colors that the current display can handle. Customize
`list-colors-sort' to change the order in which colors are shown.
If the optional argument BUFFER-NAME is nil, it defaults to *Colors*.
If the optional argument CALLBACK is non-nil, it should be a
function to call each time the user types RET or clicks on a
color. The function should accept a single argument, the color name.