  We present predictions of Spectral Energy Distributions (SEDs), from the UV
to the FIR, of simulated galaxies at $z=0$. These were obtained by
post-processing the results of an N-body+hydro simulation of a small
cosmological volume, that uses the Multi-Phase Particle Integrator (MUPPI) for
star formation and stellar feedback, with the GRASIL-3D radiative transfer
code, that includes reprocessing of UV light by dust. Physical properties of
galaxies resemble observed ones, though with some tension at small and large
stellar masses. Comparing predicted SEDs of simulated galaxies with different
samples of local galaxies, we find that these resemble observed ones, when
normalised at 3.6 $\mu$m. A comparison with the Herschel Reference Survey shows
that, when binning galaxies in Star Formation Rate (SFR), average SEDs are
reproduced to within a factor of $\sim2$ even in normalization, while binning
in stellar mass highlights the same tension that is present in the stellar mass
-- SFR plane. We use our sample to investigate the correlation of IR luminosity
in Spitzer and Herschel bands with several galaxy properties. SFR is the
quantity that best correlates with IR light up to $160\ \mu$m, while at longer
wavelengths better correlations are found with molecular mass and, at $500\
\mu$m, with dust mass. However, using the position of the FIR peak as a proxy
for cold dust temperature, we assess that heating of cold dust is mostly
determined by SFR, with stellar mass giving only a minor contribution. We
finally show how our sample of simulated galaxies can be used as a guide to
understand the physical properties and selection biases of observed samples.
