I thought that this had been addressed when I last checked this - but that was with Text Colors - appears that we need to do the same here - I thought that using Near Black (RGB 15,15,15) would work but it appears not - I think that we must be applying a Transparency to the Hatch when you select Solid because it is Grey on a White Background but Black on a Black Background - The grey is caused by the White shining through the Black which means it has a Transparency Setting that is not exposed.
The Linestring point that Marian raises is because the Closed Flag and Solid Fill only applies to a single line whereas the Hatch is something that can be applied to multiple lines and it creates the internal boundary lines for you automatically to allow for Holes etc.
If you want Islands in Holes then do a second level Hatch on the Islands in the Holes
I have logged in the issues here
Alan