Main menu colour when hovering over sub menu

Hi,

I’m having a bit of a fight with the menu coloration on a Nirvana-based site I’m working on. I can change all the hover elements, etc, with CSS except for the state of the main menu item when I hover over the sub-menu items.

To clarify:

Here’s what it should (and does) look like when I hover over the main menu item: http://picpaste.com/3a75e012d320a26895e7d6373f741e61.png

But here’s what it looks like when I scroll down and mouse over the sub-menu: http://picpaste.com/Screen_Shot_2015-04-03_at_22.59.40-d27dIlYu.png

The main menu defaults back to the green, but keeps the grey background.

I might settle for it returning to green on white, but ideally it’d stay white-on-grey.

I suspect I’m missing something regarding hover/active/etc, so any help much appreciated.

Thanks, Sarah