The bicolour LEDs have been used as an experiment in ground colour light signals, with three contacts (common/red/green) the signals can show red or green from the single lamp. Yes I know they are not prototypical but having tried to get my head round the mass of signals I would need for this junctio area I decided to go for modelmakers licence
Off (no power)
http://i179.photobucket.com/albums/w...n30/100108.jpg
On (red powered)
http://i179.photobucket.com/albums/w...30/1001081.jpg
The second signal is one line forward
http://i179.photobucket.com/albums/w...30/1001082.jpg