Color-magnitude diagram (using Gaia photometry) of stars located within 4.5 degrees from the center of the Per OB1 association. Colored stars shows the stars in our sample, gray circles represent the remaining stars from Gaia, green diamonds show 17 blue and red supergiants quoted in the literature for which we lack spectra (see the last part of Table A.1). Two isochrones and a reddening vector are also included for reference purposes. See Sect. 4.3 for explanation.