You can achieve this by using blended lines made into an Art Brush. Make a series of blends between black or gray and white, with spacing and highlighting as desired. It can look like the top group in the figure below. Then drag the collection to the Brush panel and select Art Brush from the dialog. Use Tints and Shades to color the brush by changing the color of the line's stroke.
Thanks! That'll work. Again I really appreciate it.