Change the color of navigation bar (from a drop down collection)

Hello,

I am an artist updating my portfolio website. I created a drop down menu titled "BOOKS" in my top navigation bar. Now when you go to any of the pages under "BOOKS" a new sub navigation bar appears on the top of the page. Please see my attached image.  

This new bar is grey and I do not want that. I want it to be white. I sent this question to Squarespace help and they responded that their is not a setting in the website editor that can change this. I was advised to post here to perhaps find custom code to help. Any thoughts?

Any help would be GREATLY appreciated :)

The url for the page(s) in question: 
https://www.francisvallejo.com/jazz-day
https://www.francisvallejo.com/about

Be well!

*PS. I scanned the forums to see if this was posted before, and I saw a lot of posts on how to change your drop down menu, but nothing for this grey bar. 

Bump.

21 hours ago, ndballa24 said:

Bump.

What is the website URL?

Here it is. Thanks!

The url for the page(s) in question: 
https://www.francisvallejo.com/jazz-day
https://www.francisvallejo.com/about

You can use this code to Website Tools > Custom CSS

div#folderNav {
    background-color: white !important;
}

Thank you @tuanphan !