[metapost] background and non-rgbcolors

[Taco Hoekwater]

Stephan Hennig wrote:
> Hi,
> 
> the internal variable background seems only to accept rgbcolor values
> (which is not documented).  Would it be possible to make 'background'
> accept cmykcolor or greyscale values as well?

background is simply a variable defined in plain.mp. If you want it
to be different, redefine it. A simple statement will do:

   cmykcolor background;

This usage is the reason why withcolor is polymorph.

Cheers, Taco