To change the background color in Google Docs, go to File > Page setup and select a color from the page color section, either choosing from pre-set options or entering a custom hex code. It's recommended to choose high-contrast colors for improved readability. Additionally, you can set the default background color for new documents by clicking Set as default. While this feature allows for customization, some settings like adding page borders require manual insertion every time, prompting users to create templates that can be autopopulated using Zapier.