  This paper uses radial colour profiles to infer the distributions of dust,
gas and star formation in z=0.4-1.4 star-forming main sequence galaxies. We
start with the standard UVJ-based method to estimate dust extinction and
specific star formation rate (sSFR). By replacing J with I band, a new
calibration method suitable for use with ACS+WFC3 data is created (i.e. UVI
diagram). Using a multi-wavelength multi-aperture photometry catalogue based on
CANDELS, UVI colour profiles of 1328 galaxies are stacked in stellar mass and
redshift bins. The resulting colour gradients, covering a radial range of
0.2--2.0 effective radii, increase strongly with galaxy mass and with global
$A_V$. Colour gradient directions are nearly parallel to the Calzetti
extinction vector, indicating that dust plays a more important role than
stellar population variations. With our calibration, the resulting $A_V$
profiles fall much more slowly than stellar mass profiles over the measured
radial range. sSFR gradients are nearly flat without central quenching
signatures, except for $M_*>10^{10.5} M_{\odot}$, where central declines of
20--25 per cent are observed. Both sets of profiles agree well with previous
radial sSFR and (continuum) $A_V$ measurements. They are also consistent with
the sSFR profiles and, if assuming a radially constant gas-to-dust ratio, gas
profiles in recent hydrodynamic models. We finally discuss the striking
findings that SFR scales with stellar mass density in the inner parts of
galaxies, and that dust content is high in the outer parts despite low
stellar-mass surface densities there.
