Yup, that must be it...
Per:
Allows a set of PWM pins to mirror the functionality of the on-board RGB LED.
Well... that's a bummer. I'm guessing the only way around this is to update the carrier board. 
Oh well... maybe I'll make a dedicated P2 carrier board right away instead of using the Photon2 on a repurposed Boron designed carrier board. Thanks @ScruffR for pointing that out!