& Catelan 2011) on a short timescale ($t\leq100$ Myr) in environments enriched by material polluted by AGB stars (Ventura et al. 2002) or fast rotating stars (Decressin et al. 2007). As highlighted before, Helium has been proposed also by G10 to be the possible HB [*third parameter*]{}.\
As in Paper I, we have compared our photometric data with a suitable set of BaSTI[^6] $\alpha$-enhanced HB tracks (Pietrinferni et al. 2006). We have considered theoretical models for \[Fe/H\] =$-$1.62, which is the closest value available in the BASTI database to the clusters spectroscopically determined \[Fe/H\].

In our analysis we take advantage of all initial He-abundances available in the BaSTI database, i.e. Y=0.246, 0.300, 0.350 and 0.400. Bolometric corrections and extinction effects have been calculated as in Paper I.

Recently, Gratton et al. (2011) have found spectroscopical evidence of a moderate Na-O anti-correlation in stars belonging to the HB of NGC2808, at ${\rm T_{\rm eff}}$ below $\sim$12000, that marks the onset of radiative levitation effects (see discussion below). A similar result has been found for M 4 by Marino et al. (2011), the general trend being that the bluer HB stars are on average more Na-rich and O-poor. As a consequence of 