The GE bulb number that Lionel used was 432, which is an 18 volt, .25 amp, screw based bulb with a G4-1/2 glass.
The suffixes "R" and "G" mean red and green (opaque)
The suffixes "TR" and "TG" mean transparent red and green
I've seen bulbs that appear to be original in both finishes.
I have also seen GE bulb boxes marked "OR" for opaque red.
1455 bulbs were commonly substituted for 432 bulbs at one time. I still see them on EBay, misidentified as 432.
Madison Hardware (NYC) painted them, and sold them as clear, opaque red and opaque green. They also put a dimple in the top. and sold them as beacon bulbs.
1455 bulbs are also 18 volt, .25 amp screw based bulbs, but they have a G5 glass.
The beacon bulbs don't work very well because the dimples are poorly formed and the bulb just doesn't get hot enough.
Here are some Lionel bulb charts