CMDs of NGC 2419 and verticalised RGB colour distribution obtained through the HST observations. Panel a1: gray dots are the (m_F438W, m_F438W − m_F814W) optical CMD, black dots are the selected RGB stars. The red and blue curves are the fiducial lines adopted to verticalise the RGB sequence. Panel a2: verticalised colour distribution of the selected RGB stars. The red and blue vertical lines correspond to the red and blue curves in panel a1. Panel b1: same as in panel a1 but for the (m_F814W, C_{F336W, F343N, F438W}) CMD. Panel b2: same as in panel a2 but for the filter combination used in panel b1.