[cairo] Spot colors (and CMYK)

[ecir hana]

And before you ask, why there is not such a profile if I'm able to
compute the tintTransform...

*If* there really is no such a profile, then I think it's because a
profile is empirically derived data from measurements done by
the-more-expensive-the-better device. It is not some simply
precomputed tint values of an ideal printer. So yes, you would need to
measure every possible spot color and all its intensities to create a
proper profile. Which might very well happen (for small number of
spots - but don't even think of printing more than one spot at a time)
now that I think of it but I'm almost willing to bet, that such
profile are very expensive, if accessible to general public at all.