Calibration of the color transformations from B − V to G_BP − G_RP in Eq. (A.3) and vice versa in Eq. (A.4). Panel a: Color-Color diagram for the Hyades (red), the Pleiades (yellow), and the calibration by PM13 (blue). The same Color-Color diagram, but with switched axes, is shown in panel b. Overplotted are the relationships between the two colors as derived. Panels c and d: residuals between the calculated and measured color for both transformations. The subgiants of Ru147 (encircled) do not follow the same relation, as expected. We note that the small horizontal structures in panel a, and their equivalents in the other panels originate from stars with multiple entries in WEBDA.