Near-infrared color–color diagram. The main-sequence is marked by a thick solid line, the giant branch with dotted line (Koornneef 1983), the reddening path with dashed lines (Cardelli et al. 1989), and the T Tauri locus with dash-dotted line (Meyer et al. 1997). Open symbols: quiescent colors; filled symbols: outburst colors. Source of data: Kenyon et al. (1991) for V1057 Cyg, Acosta-Pulido et al. (2007) for V1647 Ori, 2MASS PSC and Juhász et al. (2011) for EX Lup, and this work for HBC 722 and VSXJ 205126.1+440523.