Top panel: the i_LSST − y_LSST and z_LSST − y_LSST colors for the positive (colored) and negative (gray) samples in our labeled data set, with positive samples color-coded by spectral types. The 15 ultracool dwarf discoveries confirmed with Euclid spectroscopy are shown as orange stars (Section 6). For objects lacking high-S/N Euclid spectra, we identify 25 high-quality candidates based on our USMILE models, shown as blue stars (Section 7). The remaining rejected candidates are shown as black circles. Bottom panel: the z_LSST − y_LSST and y_LSST − H_VHS colors for objects plotted in the top panel.