  We present our analysis of the red-channel CoRoT data of CoRoT-2b. A deep
secondary eclipse is detected at a level of 1.02+-0.20 x10-4, which suggests
that all of the planet-signal detected previously in white light by Alonso et
al. (2009) originates from the red channel. CoRoT-2b is the coolest exoplanet
that has been detected in the optical so far. In contrast to the other planets,
its measured brightness temperature of 2170+-55 K is significantly higher than
its maximum hemisphere-averaged effective day-side temperature. However, it is
not expected that a hot Jupiter radiates as a black body, and its thermal
spectrum can deviate significantly from a Planck curve. We present models of
the planet/star flux ratio as function of wavelength, which are calculated for
a T/P profile in radiative and hydrostatic equilibrium, using a self-consistent
atmosphere code. These are compared with the CoRoT detection, and with
measurements at 4.5 and 8 um from the Spitzer Space Telescope from Gillon et
al. (2009). We estimate that reflected light contributes only at a 10-20% level
to the total optical eclipse depth. The models allow for an 'extra absorber' to
be inserted at high altitude in the planet's atmosphere. This produces a
thermal inversion layer, recently invoked to explain the photometric reversals
and flux enhancements seen in some planets in the infrared. In the 0.5-1.5 um
wavelength range, the model-spectra of planets with an extra absorber at high
altitude, are relatively suppressed in flux compared to those without such
absorber. We therefore argue that, in contrast to the other exoplanets detected
in the optical so far, CoRoT-2b may not exhibit a significant thermal inversion
in its atmosphere, causing its optical brightness temperature to be boosted
above its maximum effective day-side temperature.
