Colour magnitude plot of the 5′×5′ field-of-view centred on Wd1 utilising the photometry of Clark et al. (2005). Cluster members with both spectral types and luminosity classes are denoted as follows: RSGs and YHGs – red and yellow diamonds; B5-9 Ia⁺ – cyan diamonds; B1-4 Ia,Iab,Ib – cyan squares; O9-B0.5 Ia,Iab,Ib – blue squares; O9-B0.5 II,III – blue circles; early BHG/WNVLh – purple diamonds; WN5-8 and WC8-9 – purple circles. The vector shows the effect of differential reddening across the cluster (cf. Negueruela et al. 2010) assuming an “off-the-peg” Cardelli et al. (1989) prescription. A colour cut for cluster membership of (V − I) ∼ 4.6 as suggested by the OB (super)giants (Sect. 4.1) is also indicated.