Hi Rachel,
I believe you are correct and will need to go into the CSS or SASS to change an additional class. I don’t have the class name for you, but I suspect it is something like $navsidebar-color-selected.
To find this class name, use the f12 browser console. Safari, Chrome, Firefox, and Edge all have versions of this. Open up this console, select the element in question from the nav bar, and click on the nav bar link. I suspect a class will be added and you will need to change the color to green there as well.
Just in case you haven’t used the developer tools console before, here is a link for the Firefox version:
https://developer.mozilla.org/en-US/docs/Learn/Common_questions/What_are_browser_developer_tools
I think you are on the right track with the CSS. I took a look at one of my apps to see where the shading for the sidebar is handled and (assuming you are using the Atlas_Default layout) what I found is that the following CSS helped me:
.region-sidebar .mx-navigationtree .navbar-inner > ul > li a.active {
color: green;
}
Hopefully this gets you headed in the right direction. Good luck!