Evolution of H_δ, A × D_n(4000) planes, considering five γ values from the SFH model described in Eqs. (5) and (6) (0.5 Gyr⁻¹, 1 Gyr⁻¹, 2 Gyr⁻¹, 5 Gyr⁻¹, and 10 Gyr⁻¹). The black dots represent the spectral indices on the planes for a specific SFH and NUV −r colour. Different NUV −r colours show different spectral indices for the same SFH. The grey contours are the distribution of the spectral indices of green valley galaxies measured from SDSS spectra. The straight lines are a geometric average of the spectroscopic indices of two consecutive black dots, dividing the plane into parts and allowing us to computationally interpolate it. For different values of t_i the position of the black dots does not change considerably, demonstrating that our model is weakly dependent on the t_i parameter.