Fromleft to right panels, G, G_BP, and G_RP photometry versus external photometry: HIPPARCOS (orange), SDSS (green), PS1 (blue), OGLE (magenta). Panel a: G − r residuals of the global G − r = f(g − i) spline for SDSS and PS1, G − V residuals of the global G − V = f(V − I) spline for OGLE. Panel b: G_BP − g residuals of the global G_BP − g = f(g − i) spline. Panelc: G_RP − z residuals of the global G_RP − z = f(g − i) spline. For HIPPARCOS the residuals are computed versus the X − Hp = f(V − I) spline, where X denotes respectively G, G_BP, and G_RP. The zero point of those different residuals is arbitrary.