Richard,
The issue I think is you picked a signal icon. From your description, I
think a normal lamp would be what you are asking for. Here you would have
the active/inactive as your red/green, then the unknown/inconsistent as the
yellow. Then you don't need any logic to drive it, it follows the turnout
(or feedback sensor) directly.
-Ken Cameron, Member JMRI Dev Team
www.jmri.org
www.fingerlakeslivesteamers.org
www.cnymod.com
www.syracusemodelrr.org
Ken Cameron