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None of this matters for anyone who isn't generating print media or mastering media for wide publication:
The best workaround I have found for colour management on X11 is first and foremost to calibrate the displays themselves as close to your target colour space as possible. Then use xcalib to modify the RAMDAC data per CRTC to get even closer. That calibrates the entire display surface to your target, (ie sRGB, DCI-P3). That way when you have 2 displays side by side and you have a window half on one monitor and half on another, you still get the same output, whereas with client-side ICC correction you will get a disaster. So avoid using ICC if at all possible. Also avoid ICC if you want to be able to use screenshots as a source of content in your editing workflow. Unless you're running a Pseudocolour desktop. Client-side ICC was designed in the era of Pseudocolour (8-bit palette private colour map) and it works great there, without any compound transform artefacts.
If you want to have 2 windows on the same monitor calibrated to different target colour spaces then you need client-side ICC so they can render the difference to their windows. There isn't really any valid reason to do that, at least from a quality standpoint, while we are stuck at 8 bits per RGB. It's easier to change the colour space of the source materials to suit your (now properly calibrated) physical displays. That's what your video player will do silently when you play HDR, or even NTSC content on an X11 display.
When X11 gets around to 10 bits per RGB then it will start to make sense from a quality perspective to do the conversions at the window level, because those extra bits will avoid the errors we see today which cause banding in smooth gradients when ICC is enabled on 8 bit per RGB displays, sadly.
xcalib is currently partially borked on the Intel i965 driver, only allowing you to change the RAMDAC data for the most recently enabled display, so if you want to calibrate a multi-monitor setup you need to bring up one at a time, apply the calibration for each one at a time, and avoid using anything that adjusts global gamma, such as apps that change your colour temperature throughout the day, screensavers that use the CRTC ramps to darken the screen, and also avoid playing any 3D games that want to change display modes.
Once you figure all this out, writing a script to automate the setup when something goes wrong is pretty much your only recourse if you want to be productive.
The best workaround I have found for colour management on X11 is first and foremost to calibrate the displays themselves as close to your target colour space as possible. Then use xcalib to modify the RAMDAC data per CRTC to get even closer. That calibrates the entire display surface to your target, (ie sRGB, DCI-P3). That way when you have 2 displays side by side and you have a window half on one monitor and half on another, you still get the same output, whereas with client-side ICC correction you will get a disaster. So avoid using ICC if at all possible. Also avoid ICC if you want to be able to use screenshots as a source of content in your editing workflow. Unless you're running a Pseudocolour desktop. Client-side ICC was designed in the era of Pseudocolour (8-bit palette private colour map) and it works great there, without any compound transform artefacts.
If you want to have 2 windows on the same monitor calibrated to different target colour spaces then you need client-side ICC so they can render the difference to their windows. There isn't really any valid reason to do that, at least from a quality standpoint, while we are stuck at 8 bits per RGB. It's easier to change the colour space of the source materials to suit your (now properly calibrated) physical displays. That's what your video player will do silently when you play HDR, or even NTSC content on an X11 display.
When X11 gets around to 10 bits per RGB then it will start to make sense from a quality perspective to do the conversions at the window level, because those extra bits will avoid the errors we see today which cause banding in smooth gradients when ICC is enabled on 8 bit per RGB displays, sadly.
xcalib is currently partially borked on the Intel i965 driver, only allowing you to change the RAMDAC data for the most recently enabled display, so if you want to calibrate a multi-monitor setup you need to bring up one at a time, apply the calibration for each one at a time, and avoid using anything that adjusts global gamma, such as apps that change your colour temperature throughout the day, screensavers that use the CRTC ramps to darken the screen, and also avoid playing any 3D games that want to change display modes.
Once you figure all this out, writing a script to automate the setup when something goes wrong is pretty much your only recourse if you want to be productive.
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