Hi there!

Thanks for your query.

You can change the footer color from either the Preset edit window or from custom style option. Here is screenshot for your ease:

https://prnt.sc/gRnDTz5XHEWb

https://prnt.sc/QxWyQU-X6FFb

If you want custom CSS:

#sp-bottom {
    background: #86858a !important;
}

Best Regards