Interstellar absorption from different works plotted against the E(G_BP – G_RP) colour excess derived in this work for OCs (see Sect. 5). Top: correlation between our colour excesses compared with the interstellar absorption derived from Gaia GSP-Phot Andrae et al. (2023) (grey squares) and ESP-HS (Creevey et al. 2023) (orange triangles). Bottom: $A_V^{50}$ values in the ordinate axis from Hunt & Reffert (2023), with solid symbol marking sources with good excess determination. The colour index indicates the median intrinsic colour of each OC. The black line shows a linear fit. Both panels use the same axis scales.