a) GLIMPSE CC diagram [5.8]−[8.0] versus [3.6]−[4.5] for sources within a circle of about 10′ in radius centered on N131. The classification of class I, II, and III indicates different stellar evolutionary stages as defined by Allen et al. (2004). b) 2MASS CC diagram (H − K_s) versus (J − H). The sources for classes I and II are these, detected simultaneously by J, H, K_s, 3.6, 4.5, 5.8, and 8.0 μ bands; the sources for class III are located within a circle of 2.60′ (0.5 × r_in) in a radius centered on N131. The gray squares represent the location of the main sequence and the giant stars (Bessell & Brett 1988). The parallel dotted lines are reddening vectors. The adopted interstellar reddening law is A_J / A_V = 0.282, A_H / A_V = 0.175, and A_Ks / A_V = 0.112 (Rieke & Lebofsky 1985), and the intrinsic colors (H − K_s)₀ and (J − H)₀ are obtained from Martins & Plez (2006).