We present initial results from a wide–field , multi–colour imaging project , designed to study galaxy evolution in X-ray selected clusters at intermediate ( z \sim 0.25 ) and high redshifts ( z \sim 0.5 ) .
In this paper we give blue galaxy fractions from eight X-ray selected clusters , drawn from a combined sample of three X-ray surveys .
We find that all the clusters exhibit excess blue galaxy populations over the numbers observed in local systems , though a large scatter is present in the results .
We find no significant correlation of blue fraction with redshift at z > 0.2 although the large scatter could mask a positive trend .
We also find no systematic trend of blue fraction with X-ray luminosity .
We show that the blue fraction is a function of ( a ) radius within a cluster , ( b ) absolute magnitude and ( c ) the passbands used to measure the colour .
We find that our blue fractions ( f _ { b } ) from galaxy colours close to restframe ( U - B ) _ { 0 } , f _ { b } \sim 0.4 , are systematically higher than those from restframe ( B - V ) _ { 0 } colours , f _ { b } \sim 0.2 .
We conclude this effect is real , may offer a partial explanation of the widely differing levels of blue fraction found in previous studies and may have implications for biases in optical samples selected in different bands .

While the increasing blue fraction with radius can be interpreted as evidence of cluster infall of field galaxies , the exact physical processes which these galaxies undergo is unclear .
We estimate that , in the cores of the more massive clusters , galaxies should be experiencing ram–pressure stripping of galactic gas by the intra–cluster medium .
The fact that our low X-ray luminosity systems show a similar blue fraction as the high luminosity systems , as well as a significant blue fraction gradient with radius , implies other physical effects are also important .