  It is still a matter of debate whether the properties of galaxies hosting an
Active Galactic Nucleus (AGN) are different from the properties of quiescent
galaxies. We constructed a sample of ~50 AGN at a mean redshift of <z>~0.6 that
lack a detectable optical nucleus. This characteristic allows to study the
properties of the host galaxies with much higher accuracy than in the case of
"normal" AGN which show a prominent central point source in optical images. A
comparison sample of X-ray faint, quiescent galaxies at intermediate redshifts
shows a clear bimodality in terms of both rest-frame colors and morphological
concentration indicators. In contrast to this, the AGN host galaxies comprise a
large fraction of objects that have early-type morphologies but relatively blue
rest-frame colors, possibly due to recent or ongoing star formation. A fraction
of the "optically dull" AGN in our sample show evidence for kpc-scale
absorption; low Supermassive Black Hole accretion rates are more likely in
other cases.
