  In this paper we describe a set of models to predict the colours of galaxies
over a wide range of redshifts. We present example output from the simulations,
and discuss their application to the selection of galaxies at high redshifts,
particularly through identification of the Lyman break. Additionally we
consider the optimal choices of filters for selection at a range of redshifts.
  An interface to a subset of the simulations has been made available on the
World Wide Web for the benefit of the community at the location
http://www-astro.physics.ox.ac.uk/~rejs/research/galcols.html.
