CHARTS-287: Storybook: Remove the admin color override

[adamwoodnz]

Fixes https://linear.app/a8c/issue/CHARTS-287

Why

No visible change in Storybook. Stories already render with the modern admin color (blueberry). The WordPress packages now give that color by default, so the workaround that forced it is dead code that would hide a regression if the default changed again.

Important

Stacked on #53004 (Renovate: Update wordpress monorepo), which bumps storybook to @wordpress/base-styles 13.3.0, block-editor 18.1.0 and block-library 11.2.0. Without that bump, removing the override brings back the legacy #007cba. Merge #53004 first; this PR then rebases onto trunk.

Proposed changes

• Remove the :root { @include mixins.admin-scheme(#3858e9); } override, its comment, and the now-unused @wordpress/base-styles/mixins import from projects/js-packages/storybook/storybook/style.scss.
• Add a js-packages/storybook changelog entry.

Related product discussion/links

• Added by Storybook: Use the modern admin color scheme (blueberry) by default #52849 (CHARTS-285).
• Default changed upstream in Base Styles: Default the admin theme color to Blueberry WordPress/gutenberg#83749, released in @wordpress/base-styles 13.3.0.

Does this pull request change what data or activity we track or use?

No.

Testing instructions

1. Check out this branch, run pnpm install, then pnpm --dir projects/js-packages/storybook storybook:dev.
2. Open Charts › Bar Chart › Default and Charts › Pie Chart › Default. In the preview iframe DevTools, getComputedStyle(document.documentElement).getPropertyValue('--wp-admin-theme-color') is #3858e9.
3. Set the adminColorScheme control to midnight or light: the chart scope ([data-testid=charts-scope]) resolves to #cf4339 or #007cba.
4. Set themeName to custom with an accent color: the chart scope resolves to that accent.

Verification

Ran locally with Playwright against the Storybook from this branch:

Story	:root	Chart scope
Bar › Default	#3858e9	#3858e9
Pie › Default	#3858e9	#3858e9
Bar, adminColorScheme: midnight	#3858e9	#cf4339
Pie, adminColorScheme: light	#3858e9	#007cba
Bar, themeName: custom, accent #ff0000	#3858e9	#f00

stylelint passes on the changed file. No screenshots, because the rendered output is the same as before.

🤖 Generated with Claude Code

[github-actions]

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[adamwoodnz]

@claude please review this PR. Get the change set with a single gh pr diff 53340, then read only the changed source files it touches. Skip changelog entries and lockfiles. Use at most about 20 tool calls, and post your review before you reach that, even if it is incomplete.

[adamwoodnz]

On Claude's non-blocking notes:

1. Merge order guard: I will not add one here. The base of this PR is Update wordpress monorepo #53004, so GitHub retargets it to trunk only after Update wordpress monorepo #53004 merges. If someone reverts Update wordpress monorepo #53004 later, this PR still applies cleanly, and the result is the legacy color in Storybook only. No product code is affected. A visual check for one Storybook value is not worth its cost.
2. Rebase target: trunk is correct. gh repo view Automattic/jetpack --json defaultBranchRef returns trunk.

[adamwoodnz]

Review cycle summary

• Round reviewer: Codex, 1 round. No P1 to P3 findings, so the round phase ended early.
• Final reviewer: Claude. No blocking issues. I declined its two non-blocking notes (a guard for merge order, and a question about which branch to rebase onto) and gave the reasons above.
• CI: green (38 pass, 26 skipped).
• Resolved: I collapsed 2 review comments. There were no inline threads.
• Unaddressed human comments: none.

Merge order: merge #53004 first. GitHub then retargets this PR to trunk.

Status: clean

[LiamSarsfield]

LGTM, I checked the CSS from the pinned packages, and all seven --wp-admin-* values on :root come out the same with and without the override. With trunk's versions it drops back to #007cba, so the change is neutral once #53004 is in.

Regarding the rebasing:

• Renovate rebased #53004 this afternoon, but this branch still has the old copy, so it shows as conflicting and the Files tab has the whole bump in it.
• Rebasing onto the current renovate/wordpress-monorepo should go through cleanly. The description also links a private claude.ai session, which probably shouldn't be on a public PR.

[adamwoodnz]

Thanks for checking the CSS against both sets of versions.

• I rebased onto the current renovate/wordpress-monorepo (ace4253d0a9). The change is now the single commit bfd0e9e0c75, and the Files tab shows only the stylesheet and the changelog.
• I removed the session link from the description.