Here is the penumbra layer with a bit of the 'dead layer' started. To mix the hues for the dead layer, I've used Mars Black, Yellow Ochre, and then adding Chromium Oxide Green and Red Ochre in that order. After mixing up these hues, add Flake White to create approximately eleven shades of gray, from from light to dark, and lay them out in order from the lightest to the darkest on your palette. Mixing the black and ochre gives an olive toned dark hue; you may simply use this shade to mix with Flake White to create a full range of dark and lights, or you may also add the green and red ochre to the mix, creating a verdacchio effect. I like adding the green, (along with the red to tone down the green), to create a more olive range of grays, since the greenish hues serve as an excellent underpainting for flesh hues that will soon follow this layer.