60 μm−150 MHz colour distribution of all matches within 3′ between the RIFSCz sources (which only have IRAS observations) and LOFAR sources (yellow histogram). The dot-dashed Gaussian represents the inferred colour distribution of the true counterparts and the dashed Gaussian represents that of the random associations. The black solid line is the sum of the two. The colour distribution of the main sample is shown as the blue histogram.