Visual representation of the feature importances derived from XGBoostClassifier models trained to select quiescent galaxies using only Euclid photometry and colours (top left panel), or Euclid photometry with the addition of one ground-based optical band, and the relevant broadband colours. The optical bands are u (top right), g (middle left), r (middle right), i (bottom left), and z (bottom right). The XGBoostClassifier models were trained without foreknowledge of the redshifts.