Help needed for background colour of footer section

Hi,

I would like the bottom of my site to have a strip of blue colour.

I am trying to achieve this by making my bottom footer section have a background colour of blue. 

But for some reason, even when I select the blue theme (where the background colour is set to the blue that I want), the background of that footer section remains black. See attached screenshot to see what I mean.

If I do the same thing on the main page (outside of the footer), the blue background colour works. But just not in the footer for some reason?

Can someone shed some light on this?

The website is https://incidentzero.squarespace.com/

Thanks,
Rhonda