You need something that can be seen for some distance when it comes to rail signaling; most of the aforementioned suggestions use 5mm LEDs that when shined directly at the eyes are visible for maybe 100 yards, if you're specifically looking for it. Definitely not an option to signal an oncoming train to emergency stop.
I can envision a traffic wand-type light that uses a white plastic wand and then has the colored LEDs within; if these are Cree-type ~140 lumen color LEDs, then you're good to go, it would be like holding a small colored fluorescent tube, visible for some distance. The only catch is that you'd have to remove the wand section for using white light/using it like an actual flashlight.
A Mag host with four smaller reflectors in the head, one for each color, then some sort of unique switch, and the white wand part.. it doesn't sound too impossible..