Maybe something like this would work…
1329_offsetpathblend.ai.zip
Select the main structure, then Object/Path/Offset Path to a negative value.
Select both objects and Blend with Specified Steps.
Add points where necessary, so both objects have the same amount of points.
Set the color of the outer blend object to a darker tint color.
Set the outer object transparency of the highlight object to zero.
Vince
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