Home transparency secondary bar color

Hi there,
I need to have the secondary menu bar colour black once the header changes after displaying transparent on the home page. The rest of the site is set to how I want with the secondary bar black. It’s just on the transparent home header – the desktop is correct (transparent) and the mobile is correct with black secondary bar – it’s the sizing in between on the home page that the secondary bar isn’t showing a background of black. Hoe do I fix this?