Forensic reconstruction of galaxy colour evolution and population
  characterisation
  Mapping the evolution of galaxy colours, from blue star-forming to red
passive systems, is fundamental to understand the processes involved in galaxy
evolution. To this end, we reconstruct the colour evolution of low-redshift
galaxies, combining stellar templates with star formation and metallicity
histories of galaxies from the Galaxy And Mass Assembly survey and \shark\
semi-analytic model. We use these colour histories to robustly characterise the
evolution of red and blue galaxy populations over cosmic time. Using a Gaussian
Mixture Model to characterise the colour distribution at any given epoch and
stellar mass, we find both observations and simulations strongly favour a model
with only two populations (blue and red), with no evidence for a third "green"
population. We map the evolution of mean, weight, and scatter of the blue and
red populations as a function of both stellar mass and lookback time. Using our
simulated galaxy catalogue as a testbed, we find that we can accurately recover
galaxies colour histories up to a lookback time of $\sim6$ Gyr. We find that
both populations show little change in the mean colour for low-mass galaxies,
while the colours at the massive end become significantly redder with time. The
stellar mass above which the galaxy population is predominantly red decreases
by 0.3 dex in the last 5 Gyrs. We find a good agreement between observations
and simulations, with the largest tension being that massive galaxies from
\shark\ are too blue (a known issue with many galaxy evolution models).
