Sample stars (triangles) shown in FIR color–color diagram. Red and blue colors indicate good and moderate data, respectively. Boxes with dotted lines in Fig. 2a show different phases of dust shell evolution based on the IRAS colors. The box with a dashed line represents a region of young T Tauri stars (Harris et al. 1988). The box with a solid line in both Figs. 2a and b represents the region of RGB stars. Also, shown is Arcturus, a typical K giant (red square). In Fig. 2b, the sample is plotted using WISE 11.6 μ and 22.1 μ and IRAS 60 μ flux densities.