Upper panel: normalized histogram color distribution of stars in the HB sample (blue histogram) and RGB sample (red histogram) for NGC 5904. The RGB sample includes all the RGB stars with luminosity differing by less than ±0.1 F606W mag from the mean level of the HB. The two samples of HB and RGB stars are colored blue and red, respectively, in the lower-panel CMD, where we also show the points P _A, P _B, and P _C and the L1 and L2 segments (see the text for details).