  We reanalyse observations of type Ia supernovae (SNe) and Cepheids used in
the local determination of the Hubble constant and find strong evidence that SN
standardisation in the calibration sample (galaxies with observed Cepheids)
require a steeper slope of the colour correction than in the cosmological
sample (galaxies in the Hubble flow). The colour correction in the calibration
sample is consistent with being entirely due to an extinction correction due to
dust with properties similar to that of the Milky Way (R_B~4.6+/-0.4) and there
is no evidence for intrinsic scatter in the SN peak magnitudes. An immediate
consequence of this finding is that the local measurement of the Hubble
constant becomes dependent on the choice of SN reference colour, i.e., the
colour of an unreddened SN. Specifically, the Hubble constant inferred from the
same observations decreases gradually with the reference colour assumed in the
SN standardisation. We recover the Hubble constant measured by SH0ES for the
standard choice of reference colour (SALT2 colour parameter c=0) while for a
reference colour which coincides with the blue end of the observed SN colour
distribution (c~-0.13), the Hubble constant from Planck observations of the CMB
(assuming a flat LCDM cosmological model) is recovered. These results are
intriguing in that they may provide an avenue for resolving the Hubble tension.
However, since there is no obvious physical basis for the differences in colour
corrections in the two SN samples, the origin of these require further
investigations.
