Colour−colour diagram of all stars after correction for reddening. Stars in light grey correspond to objects sampled in the first 5′ from the cluster centre. The solid line represents the median (V − Hα)₀ colour of stars with an error on (V − Hα)₀< 0.05, and is defined as the locus of stars without Hα excess emission and hence the location of stars with EW(Hα) = 0. Objects indicated as large dots (orange in the electronic version) correspond to stars with Hα excess emission. The solid line shows the location on the CMD of atmospheric models of Bessell et al. (1998). The model is in excellent agreement with the observations. The dotted line marks the 50% completeness limit of the photometry. Spectral types are also indicated. A reddening vector proportional to E(B − V) = 0.1 (i.e. the typical uncertainty) is also shown.