a) Spitzer/IRAC [3.6]–[4.5] vs. [5.8]–[8.0] and b) [3.6]–[4.5] vs. [4.5]–[8.0] color–color diagrams. YSO candidates are selected using the criteria described in Sect. 3.1.2, and classified as class I, flat-spectrum, or class II objects by their spectral index estimated from four IRAC bands. The filled circles denote class I and flat-spectrum objects, open triangles class II objects.