SUMMARY
Color Corrections does not work in KDE Plasma5 desktop (KDE Plasma5 issue - it works in GNOME)
Recently full-upgraded from Debian GNU/Linux 9 (stretch) to Debian GNU/Linux 10 (buster)


OBSERVED RESULT
Recently full-upgraded from Debian 9 (stretch) to Debian 10 (buster).
Systemsettings/Color Corrections tab showed the following messages:
"You don't have any devices registered"
"Make sure colord module on kded is running"

kcm_colord.so was missing in /usr/lib/x86_64-linux-gnu/qt5/plugins,  it was in /usr/local/lib/x86_64-linux-gnu/plugins/kcm_colord.so
temporary copied the file to /usr/lib/x86_64-linux-gnu/qt5/plugins,  the above messages disappeared but there were no display devices to show.


STEPS TO REPRODUCE
1. 
manually built colord_kde (https://github.com/KDE/colord-kde) with cmake:
  mkdir build
  cd build
  cmake ..
  make
-lX11::X11 and -lX11::Xrandr in Link.txt in colord-kded/CMakeFiles/kded_colord.dir had to be modified to /usr/lib/x86_64-linux-gnu/libX11.so and -lXrandr, respectively)

2.
installed it with sudo make install

[sudo] password for x3k30c:
[  1%] Automatic MOC for target kded_colord
[  3%] Built target kded_colord_autogen
[ 36%] Built target kded_colord
[ 38%] Automatic MOC for target kcm_colord
[ 38%] Built target kcm_colord_autogen
[ 85%] Built target kcm_colord
[ 87%] Automatic MOC for target colord-kde-icc-importer
[ 87%] Built target colord-kde-icc-importer_autogen
[100%] Built target colord-kde-icc-importer
Install the project...
-- Install configuration: ""
-- Installing: /usr/local/lib/x86_64-linux-gnu/plugins/kf5/kded/colord.so
-- Set runtime path of "/usr/local/lib/x86_64-linux-gnu/plugins/kf5/kded/colord.so" to "/usr/local/lib/x86_64-linux-gnu"
-- Installing: /usr/local/lib/x86_64-linux-gnu/plugins/kcm_colord.so
-- Set runtime path of "/usr/local/lib/x86_64-linux-gnu/plugins/kcm_colord.so" to "/usr/local/lib/x86_64-linux-gnu"
-- Installing: /usr/local/share/kservices5/kcm_colord.desktop
-- Installing: /usr/local/bin/colord-kde-icc-importer
-- Set runtime path of "/usr/local/bin/colord-kde-icc-importer" to "/usr/local/lib/x86_64-linux-gnu"
-- Installing: /usr/local/share/applications/colordkdeiccimporter.desktop

3. 
kcm_colord.so still had to be copied:
sudo cp  /usr/local/lib/x86_64-linux-gnu/plugins/kcm_colord.so  /usr/lib/x86_64-linux-gnu/qt5/plugins/kcm_colord.so

4. 
Color Corrections tab still didn't show any display devices


EXPECTED RESULT
System Settings/Color Corrections tab should show my display device (vga-0)


SOFTWARE/OS VERSIONS

Operating System: Debian GNU/Linux 10 (buster)
Kernel Version: 4.19.0-18-amd64
OS Type: 64-bit

KDE Plasma Version: 5.14.5
KDE Frameworks Version: 5.54.0
Qt Version: 5.11.3

OpenGL vendor string: X.Org R300 Project
OpenGL renderer string: ATI RS690
OpenGL version string: 2.1 Mesa 18.3.6
OpenGL shading language version string: 1.20
OpenGL extensions:
OpenGL ES profile version string: OpenGL ES 2.0 Mesa 18.3.6
OpenGL ES profile shading language version string: OpenGL ES GLSL ES 1.0.16
OpenGL ES profile extensions:


ADDITIONAL INFORMATION
1.
before compiling colord_kde 'locate colord.so' gave:
/usr/lib/x86_64-linux-gnu/libcolord.so           
/usr/lib/x86_64-linux-gnu/libcolord.so.2
/usr/lib/x86_64-linux-gnu/libcolord.so.2.0.5
/usr/local/lib/x86_64-linux-gnu/plugins/kcm_colord.so

2.
'kcmshell5 kcm_colord' gave:
"You don't have any devices registered"
"Make sure colord module on kded is running"

3.
'journalctl -b -l -o short-monolitic'  showed nothing

4.
'systemctl status colord' or 'sudo service colord start/stop/status' gave:
   colord.service - Manage, Install and Generate Color Profiles
     Loaded: loaded (/lib/systemd/system/colord.service; static; vendor preset: enabled)
     Active: active (running) since Mon 2021-11-15 19:52:36 CET; 1s ago
   Main PID: 20368 (colord)
      Tasks: 9 (limit: 3409)
     Memory: 16.9M
     CGroup: /system.slice/colord.service
             ├─20368 /usr/lib/colord/colord
             └─20372 /usr/lib/colord/colord-sane

  Nov 15 19:52:36 x3k30c-Azalia systemd[1]: Starting Manage, Install and Generate Color Profiles...
  Nov 15 19:52:36 x3k30c-Azalia systemd[1]: Started Manage, Install and Generate Color Profiles.

5.
'colormgr get-devices' gave nothing


logging out and logging into GNOME:
'colormgr get-devices' gave:
Object Path:   /org/freedesktop/ColorManager/devices/xrandr_Compaq_Computer_Company_COMPAQ_S710_007CG65KOY15_x3k30c_1000
Owner:         x3k30c
Created:       November 15 2021, 07:52:28 PM
Modified:      November 15 2021, 07:52:28 PM
Type:          display
Enabled:       Yes
Embedded:      No
Model:         COMPAQ S710
Vendor:        Compaq Computer Company
Serial:        007CG65KOY15
Seat:          seat0
Scope:         temp
Colorspace:    rgb
Device ID:     xrandr-Compaq Computer Company-COMPAQ S710-007CG65KOY15
Profile 1:     icc-457b374109e2e61824da849371936f95
               /home/x3k30c/.local/share/icc/edid-2bcc921653f45f74328fd14c74aa2a6e.icc
Metadata:      XRANDR_name=VGA-0
Metadata:      OutputPriority=primary
Metadata:      OwnerCmdline=/usr/lib/gnome-settings-daemon/gsd-color
Metadata:      OutputEdidMd5=2bcc921653f45f74328fd14c74aa2a6e

Running systemsettings5 from GNOME results in the vga device shown.

related reports:
https://bbs.archlinux.org/viewtopic.php?id=195143
https://forums.debian.net/viewtopic.php?f=6&t=144472