Colour-colour diagrams of newly discovered quasars and other candidates. Left: I_E − Y_E versus Y_E − J_E colour-colour diagram. Right: J_E − H_E versus Y_E − J_E colour-colour diagram. The red stars mark the new Euclid quasars presented in this work, the grey circles denote the identified contaminants, and the violet circles are those marked as inconclusive or no detection (see Sect. 5.2). The red curve indicates the mean colour track of high-z quasars based on the synthetic quasar samples (the red points; Yang et al., in prep.), with redshifts of 7.0, 7.5, 8.0, and 8.5 annotated. The light blue curve represents the empirical brown-dwarf colour track from Euclid Collaboration: Barnett et al. (2019), with selected spectral types (M0, L0, T0) labelled.