infrared excess. The three groups of sources appear well separated in the \[3.6\]-\[4.5\] vs. \[4.5\]-\[8.0\] two-color diagram.

![Color-color diagrams for YSO sources in the DR15 region, Class I sources are marked with a red dot symbol; Class II sources are marked with a green dot symbol; Class III sources are indicated with a blue dot symbol. Sources marked with gray dot symbols are sources in the field without a YSO designation and photometric errors less than 0.1 mag in all bands. a) $J-H$ vs. $K-[4.5]$ two-color diagram. The solid curve is a model for dwarf main sequence population from the Dartmouth [@Dotter:2008aa] grid; the solid line at its right side is the Classic T-Tauri star locus [@Meyer:1997aa] adapted to this color space as in @Teixeira:2012aa. b) \[3.6\]-\[4.5\] vs. \[4.5\]-\[8.0\] two-color diagram, showing a clear separation between evolutionary classes.[]{data-label="fig:diagrams"}](f4a.pdf "fig:"){width="3.0in"} ![Color-color diagrams for YSO sources in the DR15 region, Class I sources are marked with a red dot symbol; Class II sources are marked with a green dot symbol; Class III sources are indicated with a blue dot symbol. Sources marked with gray dot symbols are sources in the field without a YSO designation and photometric errors less than 0.1 mag 