Mid- and far-IR SED spectral indices for stars with different disk types, classified according to their Spitzer colours. Note the degeneracy that arises between different disk structures when only simple diagrams are considered. Full disks are marked in red, PTD are marked in blue, TD are marked in green, and low excess/depleted disks are marked in pink. Circles represent detections and left/downwards pointing arrows are upper limits. Marginal detections are marked as upper limits with an additional open circle. We only include upper limits for stars with spectral types K7 or earlier, given that the data are very incomplete for M-type stars. The SED spectral indices for the models in Fig. 3 are shown as continuous lines, with arrows marking the direction of the change when various disk properties are modified (see legend).