Here are some techniques and tips.
Conical Fill: Center the conical fill over the circle, extend the diameter, and double click on the fill path semi-circle to add extra color points. I have applied this to just the selected section.
Four Color Fill: Apply to one section at a time and you can use four different colors to get a mesh fill effect.
Bitmap Copy: Create a Bitmap Copy, True Color + Alpha and use the Photo Enhance tools to make the bitmap a few shades darker. Send the bitmap copy to the back. Select the original colored sections and apply Feathering.
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