Why is the favourite star in Edge a solid colour?

You may have noticed that when you visit websites using Microsoft Edge, there is an option to add that website to your favourites.
This option is via an icon at the right hand side of the Internet address bar or URL bar.
You may also have noticed that some stars for websites are a solid colour.
The reason for the two types is that if the star is filled in then it means you have already added that webpage to your favourites.
Clicking the filled in star lets you edit your favourite.