  We use the GALFORM semi-analytical galaxy formation model implemented in the
Planck Millennium N-body simulation to build a mock galaxy catalogue on an
observer's past lightcone. The mass resolution of this N-body simulation is
almost an order of magnitude better than in previous simulations used for this
purpose, allowing us to probe fainter galaxies and hence build a more complete
mock catalogue at low redshifts. The high time cadence of the simulation
outputs allows us to make improved calculations of galaxy properties and
positions in the mock. We test the predictions of the mock against the Physics
of the Accelerating Universe Survey, a narrow band imaging survey with highly
accurate and precise photometric redshifts, which probes the galaxy population
over a lookback time of 8 billion years. We compare the model against the
observed number counts, redshift distribution and evolution of the observed
colours and find good agreement; these statistics avoid the need for
model-dependent processing of the observations. The model produces red and blue
populations that have similar median colours to the observations. However, the
bimodality of galaxy colours in the model is stronger than in the observations.
This bimodality is reduced on including a simple model for errors in the
GALFORM photometry. We examine how the model predictions for the observed
galaxy colours change when perturbing key model parameters. This exercise shows
that the median colours and relative abundance of red and blue galaxies provide
constraints on the strength of the feedback driven by supernovae used in the
model.
