[SiriusHardware]

By green, do you mean bold green or turquoise blue-green?

If bold green, that just means that green LEDs were used in the display module instead of red ones. The colour is determined by how the LEDs are made.

There are other types of display which are sometimes used in clock radios which typically have a pale blue or greenish blue hue, sometimes with orange elements or indicators. These would be Vacuum fluorescent Displays, a completely different display technology. They were not especially common in clock radios and were more often found in Hi-Fi equipment and video recorders.

Edit: Crossed with others