  We apply the 3D dust radiative transfer code SKIRT to the low-redshift
($z\leq0.1$) galaxy population in the TNG100 cosmological simulation, the
fiducial run of the IllustrisTNG project. We compute global fluxes and spectral
energy distributions (SEDs) from the far-ultraviolet to the sub-millimeter for
$\approx\,$60 000 galaxies. Our post-processing methodology follows the study
of Tr\v{c}ka et al. (2022) of the higher-resolution TNG50 simulation. We verify
that TNG100 reproduces observational luminosity functions at low redshifts to
excellent precision, unlike TNG50. Additionally, we test the realism of our
TNG100 plus SKIRT fluxes by comparing various flux and color relations to data
from the GAMA survey. TNG100 broadly reproduces the observed distributions, but
we predict ultraviolet colors that are too blue by $\approx\,$0.4 mag, possibly
related to the extinction in the star-forming regions subgrid model not being
selective enough. Furthermore, we find that the simulated galaxies exhibit
mid-infrared fluxes elevated by up to $\approx\,$0.5 mag that we attribute to
overly effective stochastic heating of the diffuse dust. All synthetic
broadband fluxes and SEDs are made publicly available in three orientations and
four apertures, and can readily be used to study TNG100 galaxies in a mock
observational fashion.
