  A new serendipitous XMM survey in the area of the Sloan Digital Sky Survey is
described (XMM/SDSS), which includes features such as the merging of
overlapping fields to increase the sensitivity to faint sources, the use of a
new parametrisation of the XMM point spread function for the source detection
and photometry, the accurate estimation of the survey sensitivity. About 40,000
X-ray point sources are detected over a total area of 122deg2. A subsample of
209 sources detected in the 2-8keV spectral band with SDSS spectroscopic
redshifts in the range 0.03<z<0.2, optical magnitudes r<17.77mag and
logLx(2-10keV)>41.5 (erg/s) are selected to explore their distribution on the
colour magnitude diagram. This is compared with the colour-magnitude diagram of
X-ray AGN in the AEGIS field at z~0.8. We find no evidence for evolution of the
rest-frame colours of X-ray AGN hosts from z=0.8 to z=0.1. This suggests that
the dominant accretion mode of the AGN population, which is expected to imprint
on the properties of their host galaxies, does not change since z=0.8. This
argues against scenarios which attribute the rapid decline of the accretion
power of the Universe with time (1dex since z=0.8) to changes in the AGN
fueling/triggering mode.
