CMD of synthetic clusters. Left panel: Composite CMD of the set of 14 synthetic clusters with two metallicity sequences separated by 0.15 dex (metallicities between [M/H] = −0.1 and −0.05 dex, and between [M/H] = 0.1 and 0.15 dex. An isochrone of age 2 Gyr was superimposed as reference, to show how the binary stars depart from the locus of single stars. The synthetic stars in the low- and high-metallicity sequences are shown in black and orange, respectively. Middle and right panels: Solution CMDs derived with the XL and S bins, respectively. There are more scattered sequences in the solution with the XL bins.