K versus H − K for all sources with detections in both bands (open squares). The dashed lines mark the completeness limit, whereas the thin line is the locus of the ZAMS (absolute magnitudes from Allen 1976, colours from Koornneef 1983) for the distance of Sh 2-217 (4.2 kpc). The dotted line indicates the reddening direction; the length of the line corresponds to an extinction of A_V = 30 mag. The adopted extinction law is from Rieke & Lebofsky (1985). The thick lines are isochrones for PMS stars 1 Myr old (with A_V = 0 and 10 mag, left to right) ranging from 0.1 to 6 M_⊙ (from Palla & Stahler 1999). Labeled are the two brightest stars towards the cluster, following the nomenclature adopted by Deharveng et al. (2003b).