Dopplergrams Question

[vnp85]

I think I am missing something about how the dopplergrams are created and how to interpret them, perhaps even in general, when it is about the Sun. So by convention, blue should be coming towards the viewer and red should be receding.

However, we see two kinds of shifts: we see shifts of darkness and shifts of light.

On the disk, does darkness mean receding gas is hiding bluer wavelengths (because from the photosphere's perspective, it is coming closer, it is receding from our perspective). Beyond the disk however, recession shows up as a light source in the red wing instead of the band's center?