value of ${\rm M_{HB}}$ by $\sim$0.04 $M_{\odot}$. For the blue tails we use the ($m_{F160BW},m_{F160BW}-m_{F555W}$) CMD. At fixed ($m_{F160BW}-m_{F555W}$) an increase $\Delta$\[M/H\]=0.3 decreases the derived value of ${\rm M_{HB}}$ by $\sim0.01$ $M_{\odot}$ . This means that if a larger mass loss is needed to explain the blue HB stars (compared to the mass loss needed to explain the redder population), an increase of \[M/H\] tends to reduce this mass loss difference. The second effect is on the RGB mass (hence on the absolute value of the RGB mass loss). An increase $\Delta$\[M/H\]=0.3 causes an increase of ${\rm M_{RGB}}$ by $\sim0.025$ $M_{\odot}$. The distribution of Y along the observed HBs is basically unaffected by the precise age and \[M/H\], because it is based on the variation of magnitude (in $m_{F336W}$ and $m_{F160BW}$, depending on the star colour) with Y, a differential property that is unaffected by the exact model metallicity and age.

Comparison between theory and observations
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In this section we will discuss separately the theoretical analysis of our three selected clusters. We stress again that allowing Y to vary within individual clusters, increases the number of free parameters needed to match the observed HB star distribution in the CMD. 