Infinite* colours

For any light source that emits light directly to our eyes, the colour that is perceived by our brain has three basic components, some amount of red, green  and blue. Variations in their amount help us to create various colours.

If we set the brightness of all three LEDs to be the same, then the overall colour of the light will be white. If we turn off the blue LED, so that just the red and green LEDs are the same brightness, then the light will appear yellow.

We can control the brightness of each of the red, green and blue parts of the LED separately, making it possible to mix any colour we like.

Black is not so much a color as an absense of light. So the closest we can come to black with our LED is to turn off all three colors.