Scatter plot of hardness ratios between energy bands 1 (0.2–0.7 keV), 2 (0.7–1.2 keV), and 3 (1.2–5.0 keV). Sources with ≥50 counts are shown in the color scheme of Fig. 3, fainter sources in gray. These sources show a higher dispersion and larger uncertainties. Dotted lines show, from top to bottom, expected hardness ratios for photon indices Γ_X = 1.0, Γ_X = 2.0, and Γ_X = 3.0. The absorption increases along the tracks toward the top-right corner. The majority of source hardnesses are consistent with power law spectra in the expected range of spectral shapes due to the large uncertainties. The black data point in the top-left corners displays the median uncertainties of all, including the low count sources.