Hey sorry for the lake of feedback on this topic.
I paste here the log of IRC from yesterday as it's related directly to this thread. Again thank you.

11:50<deevad> achadwick: Hey, I saw the last commits, and super to see progress on color management in Mypaint. thanks.

14:06<achadwick> Less like "management", more like "dump everything into sRGB". But it's a start.

15:25<deevad> Sure, I like this dump everything to sRGB ; I think you shouldn't fear of making old Mypaint files *.ora untagged to sRGB ( I read the comments of commits )

20:08<achadwick> Transitioning old .ora files which expect sRGB compositing to a linear compositing world is going to be even more fun :/ You can't automatically "fix" a file with 8bpc and gamma compression without losing fidelity.

20:48<deevad> oh, ok. I didn't knew it.

24:41<deevad> achadwick: Will Mypaint be also able to take the monitor calibration icc profile in account ?

27:46<achadwick> I don't think we've planned that far ahead. If the profile can be discovered, and there's a good way of making it work with Cairo, then maybe one day.

29:49<achadwick> Moving tileddrawwidget to OpenGL would be a nice thing to consider, but it'd be a lot of work and would likely get in the way of gtk3 porting (which is still unplanned; we need developer time for that)

30:28<deevad> achadwick: oh good. For the moment , I have difficulties to re-open my *.ora artwork in Mypaint after working them on Krita ; krita use only sRGB and grab the monitor calibration too. My reds and green are so different on Mypaint that I don't like to finish my artwork on it as I was used before.

31:16<deevad> one work around would be to turn of my calibration profile , but ... mheeee

31:40<deevad> XD

BTW, Krita uses linear light for compositing internally, and GIMP's GEGL-based compositing in newer versions will use linear light too, as I understand it. The difference is actually quite stark for files which use low-alpha overlays:

http://wiki.mypaint.info/Linear_light_composition

Just so you know: there will be differences remaining after the code fixing this bug is merged with MyPaint master because Krita and MyPaint composite layers slightly differently.

We definitely want a bare minimum of colour management, even if it only happens on loading images with embedded CMS chunks and we assume your display is sRGB (initially).

It's hard to get a consistent color workflow (RGB) working with Mypaint within a chain of other application with Color management especially since my workflow evolved to Mypaint<>Krita duo ( Krita is a application with color management only ). it result in subtle difference (this jpg doesn't do real justice to the difference, but the idea is here ):
http://wstaw.org/m/2012/03/10/20120310_screenshot_02.jpg

It would be great if Mypaint could support embedded image profiles and do colour correct on the fly to the monitor.

picture for test & infos :
http://www.oyranos.org/wiki/index.php?title=Main_Page
http://www.oyranos.org/wiki/index.php?title=Test_Images