No, I have 0,0,0 for all profiles. The only oddity I see is that under histogram profile I see the entry system display profile twice 
I am running darktable 3.1.0+687~g186252465
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I also have two entries of system display profile under histogram profile, I never noticed that before… Im running dt 3.0.0
How did you set up your color management? Did you use the tool @Brian_Innes mentioned above?
Is your xiccd also running as user process and your colord as system process, which Linux distro are you using?
Sorry for that many questions. But I would like to figure out where the difference is between our systems.
Obviously we both have a similar problem with our color management, similar system running, but in your case RGB values are rock solid… In contrast to mine or @Brian_Innes …
██████████████████ ████████ OS: Manjaro Linux x86_64
██████████████████ ████████ Host: MACH-WX9 M1A
████████ ████████ Kernel: 5.5.2-1-MANJARO
████████ ████████ ████████ Uptime: 9 hours, 50 mins
████████ ████████ ████████ Packages: 1405 (pacman)
████████ ████████ ████████ Shell: bash 5.0.11
████████ ████████ ████████ Resolution: 3000x2000
████████ ████████ ████████ DE: Xfce
████████ ████████ ████████ WM: Xfwm4
████████ ████████ ████████ WM Theme: Default-xhdpi
████████ ████████ ████████ Theme: Matcha-sea [GTK2], Adwaita [GTK3]
████████ ████████ ████████ Icons: Papirus-Maia [GTK2], Adwaita [GTK3]
Terminal: xfce4-terminal
Terminal Font: Monospace 12
CPU: Intel i7-8550U (8) @ 4.000GHz
GPU: Intel UHD Graphics 620
GPU: NVIDIA GeForce MX150
Memory: 4619MiB / 15765MiB
I did nothing special, colord is run by systemd, xiccd is launched from my xfce4-session (I guess that answers your x-atom question. If not please tell me how to find that out).
Question. (Perhaps a silly one!)
Would applying a colour profile twice, be the cause of these issues with darktable reporting an incorrect colour from the colour dropper?
I’m running Linux Mint (Cinnamon), and I’ve applied my calibrated monitor colour profile using the gnome colour manager. I’ve also set darktable to use the calibrated monitor profile for the display profile. So would this mean that the colour date is getting managed twice? I.e. once by the system display profile, and again by the display profile in darktable?
I don’t think so. From the Gnome Color Manager doc:
“The GNOME Color Manager communicates the selected profiles to color-aware applications, maintaining the color across applications.”
Most of the color management I know doesn’t actually do the conversion; it just maintains the display profiles for all the connected displays and provides them to the applications, who do the heavy lifting before pushing the pixels to the display. Apple is different in that regard, and also what they’re trying to do to Wayland…
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So probably safer to set Darktable to use system colour profile then?
I think the symptoms with non-zero black RGB values are similar to this issue: Choice of display profile affects histogram, color picker values and overexposure indicators · Issue #3271 · darktable-org/darktable · GitHub
Does that look familiar? How does your display profile tone response curve look like, do the curves touch the origin? I unfortunately still haven’t found time to look for a fix and the real root cause. 
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That sounds very familiar!
Unfortunately I can’t answer your question as I deactivated my color management.
This weekend I set up a new computer (AMD Ryzen 9 3900 , x570, … super fast 
), color management is still to be set up
I had similar problems with gimp also, did you had your problem in darktable only?
I’m not very familiar with color management in Gimp. Could you please explain the steps required to reproduce similar behavior in Gimp so I could see if that happens to me too?
I started a new picture, added background color with GRB values 0,0,0 i.e. “000000”. Then added a color circle with the RGB Color “ff0000” for red.
Then just check the color values with the color picker. Black is not “000000” and red also something different…
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I guess the issue, is the actual image data showing the colours are different, or is it an issue with Darktable colour picker showing that the values of the colours are different?
Have you tested in other image editing software?
Inside Gimp, a fully black image seems to correctly show (0, 0, 0) in Gimp’s color picker for me, so no such problems here. Tried to even break it by messing with Gimp’s color management settings, but there was no ill effect. So the behavior in the GitHub issue exists in Darktable only.
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Here comes my update:
My new system is up and running 
Manjaro 5.4.22 / KDE Plasma 5.17.5/ AMD X570, with Radeon RX5700 XT
Darktable cmtest looks better:
[marco@marco-pc ~]$ darktable-cmstest
darktable-cmstest version 3.0.0
this executable was built with colord support enabled
darktable itself was built with colord support enabled
primary CRTC is at CRTC 0
CRTC for screen 0 CRTC 1 has no mode or no output, skipping
CRTC for screen 0 CRTC 2 has no mode or no output, skipping
CRTC for screen 0 CRTC 3 has no mode or no output, skipping
CRTC for screen 0 CRTC 4 has no mode or no output, skipping
CRTC for screen 0 CRTC 5 has no mode or no output, skipping
DisplayPort-2 the X atom and colord returned the same profile
X atom: _ICC_PROFILE (739200 bytes)
description: CS230 #1 2019-12-07 15-50 2.2 F-S XYZLUT+MTX
colord: “/home/marco/.local/share/icc/CS230_W520.icc”
description: CS230 #1 2019-12-07 15-50 2.2 F-S XYZLUT+MTX
Your system seems to be correctly configured
But I still have that issue with the wrong RGB values. This time only in darktable, gimp is fine…
@flannelhead seems so that I have still the same issue that you mentioned
What did you change to make this work? What tools are you using now? colord, xiccd, displaycal, xfce color management, kde color management, …?
Still seems to be an issue in Darktable 3.2.1!
I used DisplayCal to generate the color profile and activated that with the KDE system settings.
I’ve just checked: colord is running, xiccd not.
Kernel: 5.7.9-1-MANJARO x86_64 bits: 64 Desktop: KDE Plasma 5.19.3 Distro: Manjaro Linux
In the meantime I switched the graphics card twice. Now I’m using a Geforce rtx 2060 super.
I had some trouble with two different Radeons. The 5700 had screen freezes once in a while and the 570 was too slow. Well, performance on the 5700 was great
But in addition to that in darktable I could not use some modules for example local contrast or highpass. They led to strange artefacts. The nvidia is still not as fast as the 5700 but I’m much more pleased with the graphical results.
Anyway, I’m still on dt 3.0.2. Can’t say how the RGB values behave in the current version…
How can I get darktable to embed an icc in a jpg?
In the export section “profile” is set to “image settings”. But the icc is not embedded in the jpg.
I’m running 3.3.0+1484
Do I need to activate that feature somewhere else?
Found it: One needs to place a copy of the new profile in the $DARKTABLE/.config/darktable/color/out folder. Then the profile needs to be chosen in export section.
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Sorry for no answer; I attempted to look it up when you first posted, couldn’t readily find it, and subsequently got caught up in the American Thanksgiving/First Day Of Christmas Season goings on that is my family…
Don’t worry. It was your hint above that led me to the right direction… Then I just had to dig the manual. Thanks for your help!