We derive deep I band luminosity functions and colour-magnitude diagrams from HST imaging for eleven 0.2 < z < 0.6 clusters observed at various stages of merging , and a comparison sample of five more relaxed clusters at similar redshifts .
The characteristic magnitude M ^ { * } evolves passively out to z = 0.6 , while the faint end slope of the luminosity function is \alpha \sim - 1 at all redshifts .
Cluster galaxies must have been completely assembled down to M _ { I } \sim - 18 out to z = 0.6 .
We observe tight colour-magnitude relations over a luminosity range of up to 8 magnitudes , consistent with the passive evolution of ancient stellar populations .
This is found in all clusters , irrespective of their dynamical status ( involved in a collision or not , or even within subclusters for the same object ) and suggests that environment does not have a strong influence on galaxy properties .
A red sequence luminosity function can be followed to the limits of our photometry : we see no evidence of a weakening of the red sequence to z = 0.6 .
The blue galaxy fraction rises with redshift , especially at fainter absolute magnitudes .
We observe bright blue galaxies in clusters at z > 0.4 that are not encountered locally .
Surface brightness selection effects preferentially influence the detectability of faint red galaxies , accounting for claims of evolution at the faint end .