ui: Change disabled color to red

The console (linux console) doesn't differentiate between light and dark
gray.
Now red is used to signal a disabled widget.

Change-Id: I38ade5c4e04647c7794d36bc575e94819068ecb1
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1002357
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1002126
Signed-off-by: Fabian Deutsch <fabiand@fedoraproject.org>