Required:
RGB LED (4PIN)
Micro:bit
Micro:bit Breakout Board
Connect R, G, B, GND Pin to P0, P1, P2, GND respectively.
Code:
https://makecode.microbit.org/_HvJc5W8jo8P0
It shows:
Red + Green = Yellow
Green + Blue = Cyan
Blue + Red = Magenta
Red + Green + Blue = White
Further development should be the demo of different color light level.