LED stands for Light Emitting Diode. This is a lighting technology that we have seen for decades as little circles of light usually representing that a device is on… or, if the light is blinking maybe it means there is a problem or error. Green, red and yellow were the common colors and the easiest to manufacture. As soon as the first big manufacturer started using them in products the costs came down quickly and they caught on. They can be really inexpensive when you make them in large quantities (as is true with many products).
More recently manufacturers started working with other colors (like blue, which was hard to make at first); and then more products could use them, which drove the quantities up and the prices down even further.
Source: Energyemp
