Colour excesses E(G − K_S) versus E(J − K_S) for the red giants sample (left), the main sequence sample (center) and the combined sample (right). Black dots are the 1000 stars selected in each sample. Solid lines represent the colour excess increase with extinction for a reference temperature T_eff (4136 Kfor RG, red; 5550 K for MS, dark blue) and the corresponding reference colour (2.49 for RG, pink; 1.49 for MS, light blue). We note that some lines may overlap. Their cut corresponds to the interval of absorption A₀ indicated in Table 3 (13.3 for RG, 3.5 for MS).