  Photometric redshift classifiers provide a means of estimating galaxy
redshifts from observations using a small number of broad-band filters.
However, the accuracy with which redshifts can be determined is sensitive to
the star formation history of the galaxy, for example the effects of age,
metallicity and on-going star formation. We present a photometric classifier
that explicitly takes into account the degeneracies implied by these
variations, based on the flexible stellar population synthesis code of Kodama &
Arimoto. The situation is encouraging since many of the variations in stellar
populations introduce colour changes that are degenerate. We use a Bayesian
inversion scheme to estimate the likely range of redshifts compatible with the
observed colours. When applied to existing multi-band photometry for Abell 370,
most of the cluster members are correctly recovered with little field
contamination. The inverter is focussed on the recovery of a wide variety of
galaxy populations in distant (z~1) clusters from broad band colours covering
the 4000 angstrom break. It is found that this can be achieved with impressive
accuracy ($|\Delta z| < 0.1$), allowing detailed investigation into the
evolution of cluster galaxies with little selection bias.
