Chromosome maps for RGB stars in the studied clusters. Dotted lines separate between P1 and P2 according to the definition given in Milone et al. (2017). The mean photometric errors are shown in the bottom left corner of each panel. Different subpopulations identified employing a k-means algorithm are shown with different colours and symbols, as labelled. Large empty black symbols denote the mean Δ (F275W−F814W) and ΔC(F275W, F336W, F438W) values of each subpopulation. 3D chromosome maps can be visualised at these links NGC 288, M 3, NGC 2808.