Great!

Excellent! Thank you very much for your advice. It has worked, and I have been able to change the footer to the same colour as the top menu (#1E90FF, otherwise known as dodgerblue!). If you would like to see the result, here is the URL: https://peterboroughchoral.org.uk/index.php. Many thanks.

Too bad.
For design questions you should always provide a link to the problem.
An attempt:
You can try the following code in your template styles in the custom CSS:

footer {

   background-color: rgba(219, 11, 11, 0.85);

}

Thank you for offering a solution to my problem, but unfortunately the Module/Component Styling section of the Hayley template settings does not include the Footer.

Hello ! I don't have the Hayley template but in my templates I can change the background color of the footer in the options.
Template -> Your template styles -> GENERAL tab -> Module/Component Styling -> then scroll all the way down and change the module position "Foter Backround Color" to your favorite color!