We present a combined study of the colour–magnitude relation , colour distribution and luminosity function of a sample of 24 clusters at redshifts 0.3 < z < 1 .
The sample is largely composed of X–ray selected/detected clusters .
Most of the clusters at redshifts z < 0.6 
display X–ray luminosity or richness typical of poor clusters or groups , rather than the more typical , massive clusters studied in literature at redshifts z \ga 0.3 .
All our clusters , including groups , display a colour–magnitude relation consistent with a passively evolving stellar population formed at a redshift z _ { f } \ga 2 , in accordance with observed galaxy populations in more massive clusters studied at comparable redshifts .
Colours and luminosity functions show that the cluster galaxy population is consistent with the presence of at least two components : old systems formed at high redshift that have evolved passively from that epoch , together with a galaxy population displaying more recent star formation .
The former population forms at 2 \la z _ { f } \la 5 , the latter at redshifts z < 1 .
A model in which stars do not evolve is clearly rejected by both by the colour of reddest galaxies and by the characteristic luminosity m ^ { * } 
measures .
All clusters ( with one possible exception ) are detected independently by an almost three dimensional optical search employing sky position and colour – this despite the primary X–ray selection and low X–ray flux/optical richness displayed by the majority of the sample .