Unable to add presets with same slug as default preset via theme.json

[madhusudhand]

Description

Are default presets such as colors, shadows immutable? Should they?

When default presets are enabled, adding a new preset (color or shadow) with the same slug as default preset, it neither adds it to the theme presets, nor overrides the default preset.

Note: slug black is given value red for testing

Where as when default presets are disabled, it allows to add with same slug.

It is also the same case for other presets.
Are the default presets (core presets) immutable by design?

Step-by-step reproduction instructions

Add a new color or shadow preset with same slug in theme.json.
Observe that the new value (theme preset) isn't available for use.

Screenshots, screen recording, code snippet

No response

Environment info

• Wordpress 6.4
• Gutenberg trunk

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