Colour–magnitude diagram of the training sample with the expected absolute magnitude in the Gaia G-band shown in the left panel and the absolute magnitude predicted by the algorithm in the right panel. It is striking to see the RC on the predicted CMD so clearly (highlighted by the red box), while this feature it is less obvious on the expected CMD. We also highlighted with the blue rectangle the location of the BHB stars, which were added in the training sample as explained in Sect. 2.2.