CMD of M31 stars classified in the literature, using the photometry of Massey et al. (2016). Smaller markers without contours are stars present in the HST footprint but not in HST catalogues, smaller markers with grey contours are stars in HST catalogues but not in our YSG selection, and larger markers with black contours are the selected YSG candidates. The dotted lines highlight a region encompassing most of the HST-detected YSGs that are absent from our sample.