Hello @KC ,It seems you want to change the color scheme of the vendor dashboard. For that you just need to go to admin dashboard >>MultiVendorX >> Settings >> Seller dashboard , from here you can simply choose the color scheme of your choice for the vendor dashboard (http://tinyurl.com/yra6mp7g).
Now if you want to add customized color scheme on your end then you will have to add custom CSS on your end.
Let us know if you need any further assistance.