Average spectral properties of our sample as a function of colour and K_Kron as a proxy of the stellar mass. Left panel: Sample divided into red (72) and blue (76) galaxies, with their stacked spectra displayed in red and blue, respectively. A (g − r)_Kron colour cut was used. The inset in the top left corner shows a colour distribution of our sample, where the x-axis represents the observed (g − r)_Kron colour, corrected for extinction. Right panel: Whole sample divided into three subclasses based on the three bins of K_Kron. In red is the stacked spectrum of the brightest galaxies with K_Kron < 17.9 mag, in green that of the galaxies with intermediate luminosity 17.9 mag ≤ K_Kron < 18.9 mag, and in blue the stacked spectrum of the faint galaxies with K_Kron ≥ 18.9 mag. In the top left corner, an inset showing the trend between (g − r)_Kron and K_Kron magnitude is reported. The dashed magenta line corresponds to the best fit of the linear correlation. In both panels, the stacked spectrum of the entire population of members (148) of MACS0416, obtained with AAOmega, is shown in black. All spectra are rest-frame and have been smoothed using a Gaussian kernel with a sigma of 2 pixels. The vertical dashed grey area corresponds to the spectral region of the join between the two arms.