I think it's presenting the same luminance map you'd see with the Alt Amount slider in Sharpening..
Select the Show Luminance Mask check box to view the luminance information of the photo in black and white representation. The part in red color shows the actual area masked by the Luminance Range Mask.
So Richard is right with no Hue, but also no Saturation.
Sean McCormack. Author. Magazine Writer. Former Official Fuji X-Photographer.