Here is the latest effort, the paintwork needs a touch up and some weather, but best done when on the layout. The signal arms are Mark Tatlow's Highland Rly, the rest is brass bar and strip etc.
So we have a single head, two aspect, colour light signal with red / green LEDs for illumination (design by @Pete Harvey and kit from C&L Finescale)... we are thinking that operating the signal from DCC ought to be possible. I have looked at the range of decoders on the DCC Supplies web site...