(In reply to comment #1)
> It looks like g_dbus_connection_register_object() is returning 0 and not
> setting a GError... Do you have any critical warnings on the console when you
> run /usr/libexec/colord manually?

I cannot see any critical messages when running it manually.

$ LANG=C sudo /usr/lib/i386-linux-gnu/colord/colord -v
14:18:26	Verbose debugging enabled (on console 1)
14:18:26	CdMappingDb: trying to open database '/var/lib/colord/mapping.db'
14:18:26	CdDeviceDb: trying to open database '/var/lib/colord/storage.db'
14:18:26	CdMain: acquired name: org.freedesktop.ColorManager
14:18:26	new profile (/usr/share/color/icc/pigment/CMY.icm) has no DICT tag
14:18:26	/usr/share/color/icc/pigment/CMY.icm has no profile-id nor FILE_checksum, falling back to slow MD5
14:18:26	CdProfileStore: parsed new profile '/usr/share/color/icc/pigment/CMY.icm'
14:18:26	CdProfileStore: emit added (and changed): /usr/share/color/icc/pigment/CMY.icm
14:18:27	CdMain: Adding profile /org/freedesktop/ColorManager/profiles/icc_781f6f71344167d3526631689139f109
14:18:27	CdMain: Emitting ProfileAdded(/org/freedesktop/ColorManager/profiles/icc_781f6f71344167d3526631689139f109)
14:18:27	new profile (/usr/share/color/icc/pigment/fogra27l.icm) has no DICT tag
14:18:27	/usr/share/color/icc/pigment/fogra27l.icm has no profile-id nor FILE_checksum, falling back to slow MD5
14:18:27	CdProfileStore: parsed new profile '/usr/share/color/icc/pigment/fogra27l.icm'
14:18:27	CdProfileStore: emit added (and changed): /usr/share/color/icc/pigment/fogra27l.icm
14:18:27	CdMain: Adding profile /org/freedesktop/ColorManager/profiles/icc_e729b445abc89051fe8ba7c6d8e9b127
14:18:27	CdMain: Emitting ProfileAdded(/org/freedesktop/ColorManager/profiles/icc_e729b445abc89051fe8ba7c6d8e9b127)
14:18:27	Adding metadata CMF_version=0.1.20
14:18:27	Adding metadata CMF_binary=../client/cd-create-profile
14:18:27	Adding metadata CMF_product=colord
14:18:27	CdProfileStore: parsed new profile '/usr/share/color/icc/colord/crayons.icc'
14:18:27	CdProfileStore: emit added (and changed): /usr/share/color/icc/colord/crayons.icc
14:18:27	CdMain: Adding profile /org/freedesktop/ColorManager/profiles/icc_0f39f5fa24e4d40877f5e3041a8ce646
14:18:27	CdMain: Emitting ProfileAdded(/org/freedesktop/ColorManager/profiles/icc_0f39f5fa24e4d40877f5e3041a8ce646)
14:18:27	Adding metadata CMF_version=0.1.20
14:18:27	Adding metadata CMF_binary=../client/cd-create-profile
14:18:27	Adding metadata CMF_product=colord
14:18:27	CdProfileStore: parsed new profile '/usr/share/color/icc/colord/x11-colors.icc'
14:18:27	CdProfileStore: emit added (and changed): /usr/share/color/icc/colord/x11-colors.icc
14:18:27	CdMain: Adding profile /org/freedesktop/ColorManager/profiles/icc_bb61e89d71848368bd09d855b5ce4478
14:18:27	CdMain: Emitting ProfileAdded(/org/freedesktop/ColorManager/profiles/icc_bb61e89d71848368bd09d855b5ce4478)
14:18:27	CdProfileStore: failed to open: Error opening directory '/usr/local/share/color/icc': No such file or directory
14:18:27	CdProfileStore: failed to open: Error opening directory '/Library/ColorSync/Profiles/Displays': No such file or directory
14:18:27	CdProfileStore: failed to open: Error opening directory '/var/lib/colord/icc': No such file or directory
14:18:27	CdProfileStore: failed to open: Error opening directory '/var/lib/color/icc': No such file or directory
14:18:27	CdDeviceDb: get devices
14:18:27	failed to find profile /usr/share/color/icc/Argyll/ClayRGB1998.icm for override
14:18:27	failed to find profile /usr/share/color/icc/Argyll/sRGB.icm for override
14:18:27	failed to find profile /usr/share/color/icc/Argyll/ProPhotoRGB.icc for override

But I do not know if the culprit event is triggered here.