Difference between microlensing colours and the spectroscopic colours versus the amount of differential reddening based on the maps by Nataf et al. (2013). The microlensing values used in the plots are based on the assumption that the bulge red clump has (V−I)₀ = 1.06 and M_I = −0.12. The stars have been colour coded according to their surface gravities (as shown by the colour bar on the right-hand side).