I’m using GP Premium, Aspire template, with Brizy.
I edited the Elements/Headers that came with the template to work with my theme. On the Home page, the Primary Navigation menu is perfect: transparent until sticky, then turning translucent blue.
In my two headers for my body pages (Inner and Workshop), the background is translucent even before scrolling down. From what I can see, the settings for these three headers elements are identical other than using a featured image on the inner pages and a fixed one on Home.
Making a transparent background in Site Header Primary Navigation does seem to achieve the effect I want (transparent on page, not transparent on sticky toolbar). I was nervous to do that earlier when Sticky Navigation wasn’t mentioned on that screen.