Color–color diagram showing the Euclid Y_E − J_E vs. J_E − H_E color space. The grayscale background represents the density of sources from the Euclid Q1 dataset, limited to high-quality detections and magnitudes brighter than 23 mag in all three bands. Overplotted are synthetic Euclid colors of M6–T9 UCDs from the A. Sanghi et al. (2024) sample, colored by spectral type. Mid-to-late T dwarfs clearly deviate from earlier-type UCDs, forming a distinct population toward redder Y_E − J_E and bluer J_E − H_E colors. The black dashed lines indicate the adopted color selection boundaries (0.1 < Y_E − J_E < 0.9 and J_E − H_E < −0.1) used to identify candidate mid-to-late T dwarfs in the Euclid Q1 dataset.