m_F814W vs. m_F275W – m_F814W CMD (left) and m_F814W vs. C_{F275W,F343N,F435W} pseudo-CMD (middle) of stars in the central field zoomed in around the RGB. The solid aqua line plotted in the left panel is the fiducial line of the MS, SGB, and RGB. The dashed line represents the fiducial of equal-luminosity stars, and the fiducial line of binary systems composed of one MS turn-off star is plotted with the dot-dashed line. The probable RGB binaries, selected from the Δ_{F275W,F343N,F435W} vs. ${\mathrm{\Delta }}_{\mathrm{F}275\mathrm{W},\mathrm{F}814\mathrm{W}}^{\mathrm{b}\mathrm{i}\mathrm{n}}$ ChM shown in the top-right panel, are represented with magenta and grey triangles. The bottom-right panel illustrates the simulated ChM for RGB binaries composed of 1P stars (crimson) and 2P stars with intermediate (orange) and extreme (teal) chemical compositions. The grey points reproduce the observed ChM plotted in the top-right panel.