Top panel: flux distribution for the MS model with T_eff = 4621 K and log   (g) = 4.77 calculated with the CNONa2 (solid line) and the CNONa2MgAl (dotted line) metal compositions. The transmission curves for the Johnson-Cousins UBVI (thin black lines) and the Strömgren uvby filters (grey-shaded regions) are also shown. Bottom panel: relative flux difference between the two spectral energy distributions, as a function of the wavelength.