Solution (source code)

= Solution

Both operators map linear combinations of $|\psi_g\rangle$ and $|\psi_b\rangle$ to linear combinations of the same two <vectors>: $R_g$ merely changes one coefficient, while
$$
R_{|\Omega\rangle}=I-2|\Omega\rangle\langle\Omega|
$$
has $|\Omega\rangle\in P$. Therefore each leaves $P$ invariant.