  We demonstrate the use of Stimulated Emission Depletion (STED) spectroscopy
to map the electron-optical-phonon sideband of the ground state of the
radiative transition of color centers in hexagonal boron nitride emitting at
2.0-2.2 eV, with in-plane linear polarization. The measurements are compared to
Photoluminescence of Excitation (PLE) spectra, that maps the
electron-optical-phonon sideband of the excited state. The main qualitative
difference is a red-shift in the longitudinal optical phonon peak associated
with $E_{1u}$ symmetry at the zone center. We argue that this is consistent
with recent findings for a carbon-based line defect with admixture of
energetically similar excited states.
