  The $N_c$-dependence of the vertices $PPP\gamma$, where $P$ is a pseudoscalar
meson and $N_c$ is the number of colors, is analyzed with regard for the
$N_c$-dependence of the quark charges. It is shown that the best processes for
the determination of $N_c$ are the reactions $K\gamma \to K\pi$ and
$\pi^pm\gamma\to\pi^\pm\eta$ as well as the decay $\eta\ra\pi^+\pi^-\gamma$.
The measurement of the cross section $\sigma(\pi^-\gamma\ra\pi^-\eta)$ at the
VES facility at the IHEP agrees with the value $N_c=3$.
