  If dark matter is composed of neutralinos, the gamma-ray radiation produced
in their annihilation offers an attractive possibility for dark matter
detection. This process may contribute significantly to the extragalactic
gamma-ray background (EGB) radiation, which is being measured by the FERMI
satellite with unprecedented sensitivity. Using the high-resolution
Millennium-II simulation of cosmic structure formation we have produced the
first full-sky maps of the expected contribution of dark matter annihilation to
the EGB radiation. Our maps include a proper normalization of the signal
according to a specific supersymmetric model based on minimal supergravity. The
new simulated maps allow a study of the angular power spectrum of the gamma-ray
background from dark matter annihilation, which has distinctive features
associated with the nature of the annihilation process. Our results are in
broad agreement with analytic models for the gamma-ray background, but they
also include higher-order correlations not readily accessible in analytic
calculations and, in addition, provide detailed spectral information for each
pixel. In particular, we find that color maps combining different energies can
reveal the cosmic large-scale structure at low and intermediate redshifts.
