To get a perfect print preview on screen and than offset print result I think it's required to embed ICC Profiles and/or CMYK color support for any color definition inside CSS?

The on princexml.com given exsamples (Books) using front covers photos in RGB. Is that really ready for print yet. I guess there will be problems in print, if no one changes the presets to cmyk. I'm wrong?

We are still testing, at tyclipso.net

The latest alpha version of Prince 6.0 supports CMYK colors, but does not yet support CMYK images. We will be adding support for CMYK images in the future.

I would imagine most printeries now have fully colour-managed workflows with final conversion from RGB to CMYK done in RIP before it hits the platemaking machine.

The trouble with CMYK is that you are always targetting a particular press/ink/paper combinations, so after carefully tuning your CMYK PDF for a particular printery, you find that the job turns out crap at a different printery.

It is wisest to keep your graphics and publication in RGB as much as possible. What would be handy is being able to specify the ICC colour profile of the output press and for out-of-gamut colours to be marked in some way in a preview display. Customarily, this warning colour is a hideous green or magenta!

This would allow you to tweak the rendering intents of graphics individually or the publication as a whole to get the best rendering.

Today we have released Prince 6.0 rev 7, which includes support for CMYK TIFF and JPEG images.