Near- to far-infrared color–color diagrams. a) (J − H) vs. (H − K_s) diagram. Green solid lines are the loci of the main-sequence dwarfs and giant stars (Bessell & Brett 1988). The arrow shows a reddening vector of A_V = 5 mag (Rieke & Lebofsky 1985). The dot-dashed line indicates the locus of dereddened T Tauri stars (Meyer et al. 1997). The dashed lines, which are drawn parallel to the reddening vector, define the reddening band for normal field stars and T Tauri stars. Crosses are overplotted with an interval corresponding to A_V = 5 mag. b)  [3.6]  −  [4.5]  vs.  [5.8]  −  [8]  diagram. The classification scheme is based Megeath et al. (2004) and Allen et al. (2004, 2007). The arrow indicates an extinction of A_Ks = 5 mag according to Indebetouw et al. (2005). c) log[F60/F25] vs. log[F25/F12] diagram. The sample of Hii regions, T Tauri stars, Herbig Ae/Be stars, post AGB stars, and planetary nebulae are adopted from Palla et al. (1991), Zhang et al. (2006a), Zhang et al. (2006b), Suárez et al. (2006), and Tajitsu & Tamura (1998), respectively. The protostar is presented as an asterisk in all three panels.