Selected CMDs from the YSO models and classification scheme by Robitaille et al. (2006), separated according to their mass and stage of evolution. The models are at a distance of 50 kpc. The L, I, and H designations in the legend represent stars of 0.2, 2.0, and 20 ﹩{M}_{\odot }﹩, respectively. For the low and intermediate-mass YSOs, a division between sources at different evolutionary stages is seen. The massive YSOs (20 ﹩{M}_{\odot }﹩) have less definition. The distribution in luminosity is due to the initial stellar mass, with the most massive sources occupying the brighter regions of the CCDs.