Effect of offsets in the abundances of selected metals from the chemical composition of the NOM isochrone (panels (b)–(d) of Fig. 6) on the observed m_F150W2 − m_F322W2 colour of the star at T_eff = 4000 K. The effects are shown at three different metallicity offsets, where M only includes metals heavier than oxygen. Positive values indicate that the star gets redder when the abundance of the element is increased. The 0 (no-effect) horizontal line is shown for reference.