Site Editor: Background color flashes on first load

[t-hamano]

Description

When you access the Site Editor and the canvas loads for the first time, it briefly switches to a white background.

This issue does not occur in WP6.4.2 with the Gutenberg plugin disabled.

Step-by-step reproduction instructions

• Activate TT4.
• In the Site Editor, switch to a style that has a background color.
• Reload your browser.

Screenshots, screen recording, code snippet

cd8b2baf147b4fbb37d73e8b2dcd95aa.mp4

Environment info

No response

Please confirm that you have searched existing issues in the repo.

Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

Yes

[annezazu]

This issue does not occur in WP6.4.2 with the Gutenberg plugin disabled.

When can you replicate in this case?

[t-hamano]

When can you replicate in this case?

This can be reproduced when the Gutenberg plugin is enabled. At least it can be reproduced when you enable Gutenberg plugin version 17.2.2.

[t-hamano]

I went back through the commits and found that the problem occurred at #56000 (commit hash f9b544d).