fix: temporary patch BEC editor preview

[laurelfulford]

All Submissions:

• Have you followed the Newspack Contributing guidelines?
• Does your code follow the WordPress coding standards and VIP Go coding standards?
• Have you checked to ensure there aren't other open Pull Requests for the same update/change?

Changes proposed in this Pull Request:

We use the Block Editor Color plugin whenever we need to add to or override the classic theme's editor palette.

As of WordPress 7.0, the editor preview stopped working for colours overriding default colours - it still works fine for additive colours.

This has been reported to the plugin's support forum, but this PR also adds a temporary fix to the Newspack Theme (I opted to add it here so it's strictly adding to the theme's functionality -- or lack thereof. We won't need to use this plugin once we move to a block theme).

Closes NPPM-2892

How to test the changes in this Pull Request:

1. Install and activate Block Editor Colors
2. Navigate to Settings > Editor Colors.
3. Change one of the Default Colours (rather than adding a new one) and click 'Update':

4. Edit a post or page and try to apply a colour to a block.
5. Note that your updated colour appears correctly in the palette, but when you apply it to a block, it uses the original default. If you publish, the custom colour is correctly used on the front-end.
6. Apply this PR.
7. Retest the editor; confirm that your editor preview works as expected.

Other information:

• Have you added an explanation of what your changes do and why you'd like us to include them?
• Have you written new tests for your changes, as applicable?
• Have you successfully run tests with your changes locally?

[Copilot]

Pull request overview

This PR adds a temporary compatibility layer in the Newspack classic theme to ensure the Block Editor Colors plugin’s override palette CSS is applied inside the block editor iframe (WordPress 7.0+), restoring correct editor-side preview behavior for overridden default colors.

Changes:

• Add a theme-side compatibility shim that injects Block Editor Colors’ generated CSS into the editor iframe via block_editor_settings_all.
• Load the shim conditionally from the theme when the Block Editor Colors plugin is present.

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
themes/newspack-theme/newspack-theme/inc/block-editor-colors.php	Adds a block_editor_settings_all filter to append plugin-generated override CSS to the editor iframe’s injected styles.
themes/newspack-theme/newspack-theme/functions.php	Conditionally loads the new compatibility file when Block Editor Colors is detected.