Cover Block: Incorrect display of color-contrast warning

[kathrynwp]

Description

In WP 6.3-RC1, the Cover block incorrectly displays a color-contrast warning, where it did not in 6.2.2.

Step-by-step reproduction instructions

1. Activate Twenty Twenty-Three
2. Add a Cover block to a page or post
3. Add a dark background image to the block (without modifying any opacity or other settings)
4. Add some text (without modifying the default colours)

Result

This message is displayed:

This color combination may be hard for people to read. Try using a brighter background color and/or a darker text color.

Expected

No color-contrast warning should be displayed if there are no contrast issues.

Screenshots, screen recording, code snippet

6.3-RC1:

Compare to 6.2.2:

Environment info

• WP 6.3-RC1
• Twenty Twenty-Three 1.1
• No plugins active except WP Beta Tester

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

[kathrynwp]

In addition, I noticed that changing the colour of the Paragraph block within the Cover block to a colour that's actually not contrasty enough removes the contrast warning.

In other words:

The contrast warning is present when it shouldn't be, and absent when it should be there.

[richtabor]

Thanks @kathrynwp — this is a duplicate of #50531 so I'll close this one. Please feel free to add additional feedback to that issue if needed. 🙇‍♂️