Two Menu Text Link and Hover Colours

Hello,

I was wondering if it was possible to achieve two menu link colours when
using the Siteorigin-North theme. My websites menu is transparent at the
top then transitions to 50% white upon scroll.

Therefore, I would like to have the menu text colour as white when the Menu is
Transparent, then as the page scrolls and the Menu changes to 50% white the text
switches to black so it can be seen on the pages white background.
Hover colours can probably stay the consistent for both menu appearances.

Any help hugely appreciated.