Why not look at some of the really small LED's, they come in 3mm dia. and
red, green, yellow, white, and I think now blue.
There are also some really tiny led's that I have used, I believe they were
smaller than 3mm. I have bought them from JamesCo, Mouser, and
other electronics companies,
You could use them as the lights directly, as they will opearate of 3-5vdc, and at about 2-3ma. just put a resister in series for dropping the voltage, or get really fancy, and put a dc voltage regulator, so the they will not burn out, and stay at max brilliance until the operating voltage drops below about
5 VDC. I am planing to use these on one of my test engines, and put a LM317
dc voltage regulator circuit under the hood of the engine.
As I convert all my switchs to DC motor operated, I am planing to add these
tiny LEDs to each switch, to show position.