1. PWM stands for Pulse-width modulation, it sets the percentage of time that a pin is HIGH and LOW. For an LED, it sets the effective brightness.
2. The Raspberry Pi 3 B+ has 2 PWM pins, but they operate on the same channel, effectively creating 1 PWM pin.
3. We need the GPIO expander because the RGB LED needs 3 PWM pins to fully function, and the Pi only has 1 on board.
4. 7 -- red, green, blue, white (red+green+blue), yellow (red+green), purple (red+blue), and cyan (green+blue).
5. The GPIO expander communicates with the Raspberry Pi using the I2C protocol.
6. The color module takes in strings representing color in various formats (#FFF, rgb(255,255,255), and translates them into a red, green, and blue channel that our Pi and LED understand.
7. The REPL helps with debugging by letting you see and manipulate the state the bot is in. It is powerful because most robotics platforms have a way of altering the state of the code while running.