AA Tau’s color behavior. Top panel: (V, V − R_J) color–magnitude diagram. The symbols are the same as in Fig. 1. The arrow indicates the color slope expected for A_V = 2 mag of interstellar extinction. The large blue circle illustrates the bright state of the system, as recorded on 19 Nov. 1995 (from Bouvier et al. 1999). The large red circle corresponds to the deep-state photometry obtained on 23 Dec. 2011. The system becomes bluer at the faintest brightness level. Bottom panel: (J − H, H − K) color diagram. The black curve indicates the dwarf locus, and the blue dashed-dotted curve the T Tauri locus. The arrow indicates the color slope expected for A_V = 4 mag of ISM-like extinction. JHK photometry for the bright state is taken from Bouvier et al. (1999) and for the faint state from Calar Alto measurements listed in Table 1.