From a very brief look at the colord-kde code, it appears like when
colord-kde was first created, it had an optional dependency on
gnome-color-manager for color calibration. By 2013, colord-kde was
able to handle this itself. Therefore, I think the gnome-color-manager
dependency is no longer needed.

The Debian GNOME team is likely to remove gnome-color-manager from
Debian since it is unmaintained upstream and no longer used in GNOME.
This might happen in time for trixie. I'm filing a blocks bug in a
moment with more details.

Thank you,
Jeremy Bícha