r−i vs. i−J, i−H, and i−K diagrams plotted as a two-dimensional stellar density histogram on a gray scale, compared with the MS locus (dashed red line), the 10 Myr and 0.5 Myr isochrones (orange and purple lines), and the giant locus (black line) predicted by PISA models. YSOs selected with classical methods and objects selected as M-type stars are indicated with magenta and cyan symbols, respectively. The reddening vectors and the limits used for the selection of M-type stars are indicated as red arrows and green lines, respectively.