Hi there!

You can set footer bacground color from the layout builder or using the custom style in the preset tab of Template options.

https://prnt.sc/10bkw4b

https://prnt.sc/10bkunn

Or,

You can use the following code in your custom CSS:

#sp-footer {
    background-color: #0b6fec;
    height: 100px !important;
}

You will find all the related info here though:

https://www.joomshaper.com/documentation/helix-framework/helixultimate/faq-how-to-do

https://www.joomshaper.com/documentation/helix-framework/helixultimate/layout-builder

Note: Path towards custom CSS: Extensions>Templates>Styles> Click on your current default template name then choose Template Options. Then find custom CSS within the custom code.

https://prnt.sc/pu705g

https://prnt.sc/pu70zn

Best Regards