Color animation in the background

Design help General
1

Hello, I want to put a color animation in the background of my website. Example:

https://www.unitedcollective.com/

I know it’s a Java script but I have no idea how I can do it. Can someone help me?

Here is my site Read-Only: LINK
(how to share your site Read-Only link)

2

Take a look at this!