Color–color diagram (including the HAWK-I methane color) for T (green), L (black), M (magenta), K (olive green), G (blue), and F (yellow) type field sources. The photometry of S Ori 70 and 73 is plotted as red filled circles and the new T-type candidate is shown with a red filled triangle. The red open circle corresponds to the synthetic methane color of S Ori 70 derived from the Keck spectrum published in the literature (see text).