Top panel: m_F275W vs m_F275W − m_F814W CMD of the HB in NGC 6752. Each population is highlighted with the same colour code used in other part of this paper. The three lines represents the ZAHB loci of appropriate metallicity and Y = 0.25, 0.28, 0.35, respectively for the solid, dashed, and dot-dashed one. Bottom panel: Same as the top panel, but we show the stellar tracks involved in the simulations to show their evolution during and past core helium burning. For each track, the end of the core helium burning is highlighted by the coloured, solid diamonds. Tracks are coloured as their respective stellar populations.