(K_s-[24]) vs. α_IRAC diagram for sources with no IRAC disk (plus symbols), sources with IRAC anaemic inner disks (open circles), and sources with thick inner IRAC disks (filled circles). The plot is divided into nine sectors by grey dotted horizontal lines and vertical dashed lines (following Cieza et al. 2008); see the discussion in Sect. 4.2 for a detailed description of sectors (i) to (v). Sources that were identified as candidate transition disks from Fig. 10 are additionally marked by open squares.