WordPress editor background is grey using Hello with WordPress 6.3.1

[jamieburchell]

Description

With a vanilla installation of WordPress 6.3.1 and "Hello" Theme (no plugins active) the WordPress editor screen has a grey background. In WordPress 6.3.1, the background colour was white.

When adding the custom fields panel or activating a plugin such as PODS, the background colour returns to white regardless.

This trac issue seems to explain why this came up in WP 6.4 and it looks like a fix is planned for 6.4.3.

Steps to reproduce

1. Install WordPress and Hello theme
2. Add a new post or page
3. The background colour is now grey.
4. Show the custom fields panel or activate a plugin like PODS.
5. The background is now white.

Expected behavior

The background should consistently be either grey, or white. Twenty Twenty-Four sets this as grey in both situations unless "Use theme styles" is turned off from the editor preferences panel. The toggle has seemingly no effect when using Hello.