Beam-filling peak intensity at 1.3 mm $(I_{1.3\text{\hspace{0.17em}mm}}^{\text{bf,peak}})$ versus dual-band spectral index (α). The black circles with error bars show the dual-band detections in the common-beam images. Their KDE is outlined by gray contours. The dashed blue and pink lines show the 3σ detection limits at 1.3 and 3 mm, respectively. The triangles in corresponding colors show those only detected in individual bands. Top: KDE of observed spectral index shown in gray shade. Two special cases including optically thin (α ≃ 3.8) and blackbody (α = 2) emission are marked by vertical dashed black lines. The colored KDEs represent predicted α values from modified blackbody (MBB) emission. Right: observed $I_{1.3\text{\hspace{0.17em}mm}}^{\text{bf,peak}}$ is shown in gray shade. The predicted $I_{1.3\text{\hspace{0.17em}mm}}^{\text{bf,peak}}$ from the MBB emission is given in colored KDEs.