05. Once you’re satisfied that this line follows your contour closely enough, place another mesh line just above it. The purpose of this line is to isolate the first line you created. The reason for isolating the line is to prevent any colour you apply to it from bleeding into the area we need to reserve for midtones. With this done, apply the shadow colour (C = 61, Y = 39, M = 83, K = 76). Pull some of the mesh points beyond the viewable area of the path so that the gradient will blend smoothly.
06. Now our shadow is in place, we can define the upper shadow area. Select the same colour we used for the mid-tones and isolate the upper ridge line. This isolation preserves the colour under the protrusion. Be sure to mould this line to the shape of the protrusion with as few mesh lines as possible. We need to keep the mesh simple at this stage because we will build on it as we go along, and we don’t want it to be difficult to edit later.
07. With all your shadows in place, start adding in highlights. I find it useful to refer to my original sketch for the position of the highlights. With the Gradient Mesh tool, create a new mesh line contoured to the shape of the upper ridge, by adjusting the handles as you would with any regular path. Select a highlight colour (C = 5.5, M = 1.5, Y = 6.5, K = 0) and apply it to the line.