The Handlan Buck Radial Lens class lights contained an internal shutter or "blind" that rotated to block off the lens that was unwanted. As the Grande seldom ran second sections on the NG most of the time the lamps were "white" (or clear) forward. The lamps also could be spun in their brackets to turn the whole body so that the green lens would face forward.
Some of the flat top radial lens lamps were converted by the Grande from kerosene lamps, using a simple (and sort of crudely) made top. Not all of the modern day engines had flat top lamps. The last pair that 487 carried were kerosene tops.
Dressell also made a few radial lens lamps. I have one that came out of the scrap pile in ALA in the early 60's. It is different from the Handlan lamps in that the lenses were mounted to a separate collar from the lamp body. To change the lamp from white to green, you rotated the collar.