NGC 4486, NGC 4649, and NGC 4552 colour distributions in (g − z), (g − k) and (z − k). The open histogram are the colour distributions for all clusters that make the final sample, according to the criteria outlined is Sect. 2. The hashed histograms show the same distributions when only the clusters with K_err ≤ 0.1 are left in the sample and the filled histogram when only the clusters with K_err ≤ 0.05 are present.