W1–W2 IR color as a function of mass for USC members, assuming ages of 5 (Top) and 10 Myr (Bottom), for the entire sample keeping flagged sources in unWISE images (see Sect. 3.1). The solid black line represents the best-fit relation with outlier rejection applied, while the blue-shaded region corresponds to the 3σ confidence interval of the fit parameters (i.e., slope and intercept). The color scale represents the inferred excess probability, as indicated by the color bar. Red circles highlight sources with an excess probability greater than 0.5. Objects below the fitted photospheric sequence identified as outliers (P_excess > 0.5) are marked with black crosses, since they are excluded from the subsequent analysis. Background shading is used to delineate mass bins used in Figure A.3.