Change dropdown menu color

Hello, i’m making final touch of my site and one of the last thing is changing a color of dropdown menu for specific page because of background picture color.
I’ve changed the color on the header menu only for this specific page.
When i change the color on the dropdown menu, its changed for the whole site…. Tried to play with the css and page id but can’t hit the right code…
With “menu-item-id”, again its changed the color for the whole site.

Can someone help me with this issue?