After some talk with Xorg developers, they argued that needing a second layer for the colour correction would cause trouble for the missing path of higher precision than 8bpc into Xorg. This seems at least not a problem for compiz. Using OpenGL the desktop is placed as textures into the graphics buffer and the colour correction can happen on the GPU, right before putting on cable.
The next argument against ICC in Xorg came with a additional read/modify/write cycle and its inherent power and time consumption.
Last but not least synchronisation is not easier with colour conversions running here and something drawing the pixels there.
So it seems most appropriate to keep colour management inside the compositing WM, improve the specs and put some more useful code snippets into libXcm.
(edited september 10, 2010 at 15:46)