Red/green/white handheld signalling lamp

Anyone who is associated with rail heritage knows that on the professional railways in New Zealand, train crews used hand held signalling lamps that could produce red, green and white light, for use when shunting a train. The older style lamps of this type worked with a mechanical rotating filter holder to move red and green filters in front of a torch bulb when a knob was turned on top of the lamp. I’ve often thought about how easy would it be to make an electronic version out of parts.
When I first started to get interested in electronics, LEDs were only available in red and green, and didn’t put out much light. It has only been with advances in LED technology in recent years being able to invent a blue LED to make up the missing primary colour to produce white light, and being able to do it at a very high brightness, that it has been possible to easily make your own lamp that can put out a reasonable amount of light and thus be visible.
To make a handheld signalling lamp, the parts needed are basically some LEDs for each colour, batteries, switches and a case and perhaps a handle. You could use tri colour LEDs that are available and program the proportions of colours that are needed to produce red, green and white, by switching in resistors using a  multi pole rotary switch. You could also use separate red, green and white LEDs to produce the colours. My first thought is to go with the second option. Jaycar has suitable LEDs for about $4 each. I would go for the 10 mm size and possibly at least four of each colour, maybe more, or spread them out a bit. 
For switches it is a question of reasonably waterproof ones and maybe more than one. The most important colour you want to display is red, which means stop as this is the most significant safety action. The main problem with many IP rated switches is they are only SPST. Jaycar does have some momentary pushbuttons that are DPDT. These are important if you want to be sure only one colour can be illuminated at a time. There would be a toggle switch for on/off, and push buttons for green and white, wired (hopefully) so as to cut off power to other colours when one is pressed.
A case would have to be clear plastic, and there are a limited range of these from Jaycar and other suppliers. A power pack would be a battery holder to hold some AAs. 
Well that is the theory anyway and at the moment I’ll leave this idea there and spend a bit of time looking in more detail into costs and so forth.