5–40 GHz radio source color–color diagnostic plot. Note that here we extrapolate both the VLA K-band and the JVLA Ka-band observations to 28.46 GHz, the center frequency of the Planck 30 GHz band. All observations for a given source are averaged, such that each data point represents a unique source. For ease of comparison, we adopt the Massardi et al. (2011) definitions of “flat”, “steep”, “up-turning”, “inverted”, “self-absorbed” and “peaked” spectra (as defined by the dotted regions).