Determination of the BP and RP flux excess dependence on G_BP − G_RP colour and its application to define the corrected excess factor C^*. Top panel: BP and RP flux excess vs. G_BP − G_RP colour for the set of standard sources from Stetson (2000) secondary standards and Ivezić et al. (2007). The red line represents the combined fit based on two different polynomials for the bluer-end and the central region and a linear fit for the red-end. Bottom panel: corrected flux excess factor C^* vs. G_BP − G_RP colour for a set of nearby sources selected from the Gaia EDR3 archive.