Color-color diagram showing J – H versus H – K. The marker colors indicate the stages of the outburst as labeled in Fig. 5. The circle and “X” symbols are the REM photometry and the X-shooter synthetic photometry, respectively. The black tri markers indicate the colors when EX Lupi was in outburst (i.e., when ɡ ≤ 12.5 mag). In the bottom left, the light gray cross shows the median uncertainties of both photometric colors, and the arrow is the A_V = 1.1 mag extinction vector following the extinction curve of Cardelli et al. (1989). The dash-dotted line is the locus of the unreddened Τ Tauri stars (Meyer et al. 1997).