Comment 2 for bug 643168

Sorry about that.

1 Start gcm-prefs.
2 Select a device that can be profiled, ie the "Create Profile for Device" button isn't greyed out. (In my case a Canon EOS Rebel XTi)
3 Click "Create Profile for Device"

Looking at the source, src/gcm-calibrate.c gcm_calibrate_device():

        /* install shared-color-targets package */
        has_shared_targets = g_file_test ("/usr/share/shared-color-targets", G_FILE_TEST_IS_DIR);
        if (!has_shared_targets) {
#ifdef GCM_USE_PACKAGEKIT
                /* ask the user to confirm */
                dialog = gtk_message_dialog_new (window, GTK_DIALOG_DESTROY_WITH_PARENT, GTK_MESSAGE_QUESTION, GTK_BUTTONS_NONE,
                                                 /* TRANSLATORS: title, usually we can tell based on the EDID data or output name */
                                                 _("Install missing files?"));

                /* TRANSLATORS: dialog message saying the color targets are not installed */
                g_string_append_printf (string, "%s ", _("Common color target files are not installed on this computer."));
                /* TRANSLATORS: dialog message saying the color targets are not installed */
                g_string_append_printf (string, "%s\n\n", _("Color target files are needed to convert the image to a color profile."));
                /* TRANSLATORS: dialog message, asking if it's okay to install them */
                g_string_append_printf (string, "%s\n\n", _("Do you want them to be installed?"));
                /* TRANSLATORS: dialog message, if the user has the target file on a CDROM then there's no need for this package */
                g_string_append_printf (string, "%s", _("If you already have the correct file, you can skip this step."));