Light emitting diode colors
Because LEDs are inherently monochromatic, whereas light bulbs emit blackbody radiation, which (at the temperatures a typical lightbulb is at) appears as white(ish) light.

If you were to put a red filter (which lets red light through) on a green LED (which only emits green light), you'd get a black LED.

Yes, you can make a white LED and then add a filter, but it's kind of annoying (white LEDs require either a mix of RGB LEDs or added phosphors that emit white(ish) light), so if we need an LED with only a single colour, that's way easier to make than a white LED.

Changing the colour of an LED is not super difficult, now that the research has been done. It's as simple as selecting a set of inorganic materials, which set the wavelength.