On the bottom left of the board, near the power button, are LED0 through LED3. The odd numbered LEDs are blue, and the even numbered LEDs are red.

With the sharpie, carefully mark the tops of the LEDs. Alternatively, if you want to black out the lights entirely, use very small pieces of electrical tape to cover them.

It's a good idea to verify the color of each LED by powering on the headset while it's open.