  A diverse range of dust attenuation laws is found in star-forming galaxies.
In particular, Tress et al. (2018) studied the SHARDS survey to constrain the
NUV bump strength (B) and the total-to selective ratio (Rv) of 1,753
star-forming galaxies in the GOODS-N field at 1.5<z<3. We revisit here this
sample to assess the implications and possible causes of the correlation found
between Rv and B. The UVJ bicolour plot and main sequence of star formation are
scrutinised to look for clues into the observed trend. The standard boundary
between quiescent and star-forming galaxies is preserved when taking into
account the wide range of attenuation parameters. However, an additional
degeneracy, regarding the effective attenuation law, is added to the standard
loci of star-forming galaxies in the UVJ diagram. A simple phenomenological
model with an age-dependent extinction (at fixed dust composition) is
compatible with the observed trend between Rv and B, whereby the opacity
decreases with the age of the populations, resulting in a weaker NUV bump when
the overall attenuation is shallower (greyer). In addition, we compare the
constraints obtained by the SHARDS sample with dust models from the literature,
supporting a scenario where geometry could potentially drive the correlation
between Rv and B
