Colour – absolute magnitude diagram (CAMD) for the average cluster distance for NGC 6611. Errors are smaller than the respective symbol if not shown. Left: Gaia CAMD of the members with known spectral types. The O stars are shown with the open blue squares, B stars with the open orange circles, A stars with the open red stars and unclassified members in black. The two runaway O stars discussed in Sect. 6 are included. We show a reddening line for an O7 V star with R_V = 3.5, the black crosses indicate A_V = 2.0, 4.0, 6.0 and 8.0 mag from left to right. Right: extinction corrected M_V0 for the average cluster distance (R_V = 3.56; Kumar et al. 2004) against the intrinsic colour (B − V)₀ from the Guarcello et al. (2007a,b) BVI photometry. The stars are marked and coloured similarly as in the left panel. Stars with an uncertain or no spectral type are not shown. We show three PARSEC + COLIBRI isochrones with ages of 1.0, 5.0 and 10.0 Myr with the solid, dashed and dash-dotted grey lines, respectively.