Change menu color for just one topic

My overall project/theme is using green as the dominant color; however, there’s one subject on the menu bar that conceptually would be much easier to explain if I could make it red. Six menu drop-downs (also green) might have five or six topics, but one of the topics will be the same “red” topic, and it would be great if it could automatically drop down as red against all the green drop-downs–without having to be clicked on first.

Is there a stack to do this?

Or would this require hand-coding?

I think that will require some CSS

Which CSS?

Can you point me to a guide?

Thanks.

Do you have a URL we can look at? What Theme are you using?

It’s not published yet, but I’m using NCD’s Forward theme.

That’s almost impossible to say until you have a url to share and the item to target.
Basically you will have to target the corres li in the ul
you may have to use :nth-child
if you want to research try searching for Css target specific li in ul or similar