Lower bi-modality analysis. Left-hand panel: JWST CMD of NGC 6440 zoomed on the lower main sequence. The orange and green curves are the two fiducial lines adopted to verticalize the colour distribution. The error bars on the right side on the plot represent the average photometric uncertainties. Right-hand panels: verticalized colour distribution of main sequence stars in the magnitude range 22.2 < m_F115W < 23.25, shown at the top. The bottom panel shows the histogram of the same distribution. The orange and green curves display the best-fit Gaussian functions to the observed distribution, while the black one shows the sum of them.