How to change color of menu items

I have a problem that’s nagging me for a long time. How do I change the color of menu items on scroll?

I have a very light background image behind the menu. That means the menu items have to be dark to be visible.

However, the background color changes to dark when scrolled. Now the dark color of the menu items are difficult to see.

Is it possible to set the color to a different value on scroll? I’m happy with a css solution, but I can’t find what makes the color change on scroll.