Original Green, also now known as ‘light green’ had to be very carefully chosen. The shad had to be just right – not too bright, but not too dark. Not too blue, but not too yellow, either. As Frederick Rhead, the art designer of HLC, said:
With the (colors) red and blue apparently settled, we decided a green must be one of the five colors. We speedily discovered that the correct balance between the blue and the red was a green possessing a minimum of blue. We had to hit halfway between the red and the blue. We had some lovely subtle greens when they were not placed in juxtaposition with the other two colors, but they would not play in combination.
Light green is, as the name suggests, the lightest of the three vintage greens (excluding chartreuse). While you should be easily able to tell chartreuse from the other vintage greens, it can sometimes be confusing when you see a single piece.
Medium green is going to be very rare, and comparative to John Deere green. If it’s not that color, and it’s not a lime green-ish color, then it’s either light green or forest green, and it should be fairly easy to tell from there.
Light green was fired from 1936-1951, when it was retired for chartreuse.
Sources: DrivingForDeco, HappyHeidi, TexasCooking, Wikipedia