[cairo] Spot colors (and CMYK)

[Francois Robert]

Kai-Uwe Behrmann wrote :
> Cmyk and alpha is not my speciality. But I am shure this matter could 
> be further thought out. However it is not the core of Cmyk, spot
colour
> or CM support in cairo.
> Most people in the graphics world can live with that Cmyk alpha
imperfection.

Not sure about what you mean exactly here, but I suggest keeping in mind
two things:
1) PDF transparency does allow CMYK and alpha.
2) A semi-realistic on-screen rendering of Postscript or PDF needs to
deal with overprint, which in some respect behaves much like alpha +
CMYK.