Effect of metallicity on JK_s[3.6][4.5] and HK_s[3.6] color–color diagrams. Top panels: two SEDs of quiescent galaxies are shown. In particular, the magenta SED represents a population 1 Gyr old redshifted to z = 3 (i.e. z_form ≈ 6) with Z = Z_⊙, while the green line shows the SED of a population of a 1 Gyr redshifted to z = 3 (i.e. again z_form ≈ 6) with Z = 0.2 Z_⊙. Bottom: color–color plots with evolutionary tracks for star-forming and passive galaxies. Tracks representing star-forming galaxies are shown in blue and cyan, while their characteristics are shown in the inserted legends. Three tracks for quiescent galaxies are shown in magenta, dark-green and light-green for different metallicities (Z = Z_⊙, Z = 0.4 Z_⊙, Z = 0.2 Z_⊙ respectively).