  We have explored the properties of a peculiar object detected in deep optical
imaging and located at the tip of an HI tail emerging from Hickson Compact
Group 16. Using multiband photometry from infrared to ultraviolet, we were able
to constrain its stellar age to 58$^{+22}_{-9}$ Myr with a rather high
metallicity of [Fe/H] = $-$0.16$^{+0.43}_{-0.41}$ for its stellar mass of
M$_\star$ = 4.2$\times$10$^6$ M$_\odot$, a typical signature of tidal dwarf
galaxies. The structural properties of this object are similar to those of
diffuse galaxies, with a round and featureless morphology, a large effective
radius (r$_{eff}$ = 1.5 kpc), and a low surface brightness (<$\mu_{g}$>$_{eff}$
= 25.6 mag arcsec$^{-2}$). Assuming that the object is dynamically stable and
able to survive in the future, its fading in time via the aging of its stellar
component will make it undetectable in optical observations in just $\sim$2 Gyr
of evolution, even in the deepest current or future optical surveys. Its high
HI mass, M(HI) = 3.9$\times$10$^8$ M$_\odot$, and future undetectable stellar
component will make the object match the observational properties of dark
galaxies, that is, dark matter halos that failed to turn gas into stars. Our
work presents further observational evidence of the feasibility of HI tidal
features becoming fake dark galaxies; it also shows the impact of stellar
fading, particularly in high metallicity systems such as tidal dwarfs, in
hiding aged stellar components beyond detection limits in optical observations.
