Pragma Theme Colour Issue - Only Homepage Image Colour Changes

Hi, we’re experiencing an issue with the Pragma theme and would appreciate any help. This minimalist theme is designed to change all of the website’s background to a single selected colour, but it is not working correctly.

When adjusting the colour in the website-appearance-theme menu, only a small box of colour around the homepage image changes (see screen capture for details). Everything else (about 99%) of the website will not change. Instead, it remains a colour that was selected years ago.

We have uninstalled and reinstalled this theme plugin and verified that it is up-to-date. Any additional advice or troubleshooting tips to resolve this issue? Many thanks!