Polygon fill alpha not applied on legend

**Describe the bug**
fill color of the polygon looks different on the polygon than it looks on the legend:
![image](https://user-images.githubusercontent.com/1927076/78987130-67984a80-7b2d-11ea-8ca7-4142baa3f69d.png)

**To Reproduce**
use fill alpha on polygon