Top: star-formation histories (SFHs) with different mass-weighted stellar age and of the form SFR(t)∝exp^−t/τ. The line colors correspond to the stellar age reported in the legends Middle: SED models after removing emission lines for each SFHs and color-coded depending on the stellar age reported in the top panel. All SEDs are normalized to the flux density level of 46.9 nJy in the NIRCam F444W filter. The black lines show the transmission curves for F444W (left) and F770W (right) JWST filters. Bottom: flux density ratio between the F770W and F444W filters as a function of the mass-weighted stellar age.