Spitzer IRAC [3.6] vs. [3.6–4.5] colour–magnitude figure derived from the Luhman et al. (2008) photometry, with grey dots indicating the Luhman et al. (2008) identified YSOs and black squares indicating those YSOs detected with Herschel. Only those YSOs with m_3.6   μm brighter than 10 are likely to be detected with Herschel. The Herschel detected sample is complete for sources with [3.6–4.5] colour  > 0.6 and m_3.6 < 10.