I haven’t investigated this to a great extent so it might be a non-issue, but I’m wondering if there’s a slight disadvantage to using Pin 13 for the green LED.
All of the RGB LEDs are on PWM capable pins, so we will be able to individually vary their brightnesses. However, the PWM for Pin 13 uses Timer 4. Timer 4 can also be used by the speaker pins, so it’s possible that there could be problems if we want to do PWM with the speaker and control the green LED brightness at the same time.
Putting the green LED on Pin 9 (which can use Timer 1 for PWM) might avoid this potential problem. The display’s DC signal, which is currently on Pin 9, could be moved to the vacated Pin 13 without causing any issues since it’s just a basic digital output.
The red LED on Pin 10 can use Timer 1 and the blue LED on Pin 11 can use Timer 0 or Timer 1, so these are already OK.