EBC

I think I have what you are looking for.

1. Create your vector shape
2. Create a contour where you want the final color and assign the interior and exterior shape target colors.
3. Simplify the nodes in the contour so they match your original shape. If you don't the blend tool gets out of wack
4. Apply a blend. the more step the smoother the gradient. If you want it really smooth you can convert it to a bitmap and blur it then use outlines to cover the blur.

I tried to upload an image but can't. Damn Russians must be messing with the internet again, Blame Trump.