Yeah, greying out RMS could be implemented, but I thought that this way would be more intuitive, since all the buttons in the dynamics window affect what dynamic is listening for (RMS or MIDI), while the pitch following is completely unrelated to dynamics.
Greying out RMS seems counter-intuitive to me. It seems less likely to me that one would make the mental connection with the yellow curve then. But I don't know, I'm not a UX expert