1. Properties > Symbology 2. Edit Symbol�?� 3. Type: Gradient Fill Symbol 4. Intervals: a high number like 40 (draws slower with higher number) 5. Percentage: a low number about 7 6. Style: Buffered 7. Right click on Style in Color Ramp and select Properties 8. Change Color 1 to preferred outside color and Color 2 to No Color 9. OK everything and adjust values where needed.
For this exact effect, I prefer to use the buffer feature class, similar to what's outlined in the blog reference above (which unfortunately just links you to the current blog entry, not the archived reference).
You will have much more control over this compared with using the gradient fill.