Upper panel: F_X in the 0.5−10 keV band vs. the [4.6]−[12] μm mid-infrared color. Selected BZBs are classified as HBLs and LBLs and are marked in green and orange, respectively. Dashed lines indicate regression lines for LBLs (purple), HBLs (red), and the whole sample (black). Lower panel: F_X in the 0.5−10 keV band vs. the α_γ as reported in the 3FGL. Solid black lines mark the area within one standard deviation centered on the mean, and solid gray shows the area computed with the median absolute deviation centered on the median value.