fix: darken light-mode green0 to #F0FFF9 for stronger positiveWash contrast

[nicoledbelcher]

Summary

Update the light-mode green0 spectrum value from #F5FFFB (rgb 245,255,251) to #F0FFF9 (rgb 240,255,249) so the positiveWash token has stronger contrast against the default light background, while still clearing WCAG AA contrast against green60 foreground.

Light-mode tokens that automatically pick up the slightly darker tint:

• bgPositiveWash (consumer-facing wash, e.g. background="bgPositiveWash" on a Box/HStack/etc.)
• accentSubtleGreen
• Tag low-emphasis green tone (via packages/common/src/tokens/tags.ts -> low.green.background -> green0)

Linear: CDS-1583

WCAG AA contrast check (green60 #098551 foreground on green0 background)

green0 value	Contrast ratio	WCAG AA (>= 4.5)
#F5FFFB (previous on master)	4.588	passes
#F0FFF9 (this PR)	4.543	passes
#EBFFF7 (originally proposed in CDS-1583)	4.499	fails by 0.001

The originally aligned value #EBFFF7 was caught by axe in CI (Storybook A11y Tests failed on Tag.stories.tsx > All, ListCell.stories.tsx > CondensedListCell, and ComponentConfigProvider.stories.tsx > Default). #F0FFF9 is the slightly more conservative compromise that still meaningfully darkens the wash without regressing the Tag low-emphasis green tone.

Scope

Modified (7 files):

• Default themes: packages/{web,mobile}/src/themes/defaultTheme.ts
• Coinbase themes: packages/{web,mobile}/src/themes/coinbaseTheme.ts
• Custom theme stories: packages/web/src/__stories__/componentConfigStickerSheet/customTheme.ts, packages/mobile/src/system/__stories__/componentConfigStickerSheet/customTheme.ts
• vscode-plugin: packages/vscode-plugin/src/cds-next/styles/spectrum.ts

Intentionally NOT changed:

• High-contrast themes (defaultHighContrastTheme.ts, coinbaseHighContrastTheme.ts on both web and mobile) remain at the previous green0 value #F5FFFB.
• Dark spectrum is untouched everywhere.
• No CDS component (Banner, MessagingCard, ContentCard, etc.) currently hardcodes bgPositiveWash in a built-in variant, so this change benefits consumer-side surfaces that opt into the token via style props.

Test plan

• yarn nx run web:typecheck - passes
• yarn nx run mobile:typecheck - passes
• yarn nx run vscode-plugin:typecheck - passes
• yarn nx format:write on modified files
• WCAG AA contrast check against green60 foreground (4.543 >= 4.5)
• Visually verify in Storybook the new wash tint reads better in consumer-style surfaces that use <Box background="bgPositiveWash">.
• CI Storybook A11y Tests now passes (was failing with #EBFFF7).

[cb-heimdall]

✅ Heimdall Review Status

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CODEOWNERS	✅ See below

✅ CODEOWNERS

Code Owner	Status	Calculation
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[nicoledbelcher]

Heads up on CI: the single Storybook A11y Tests failure on this PR is an unrelated flake, not a regression from the green0 change.

• Failing test: packages/web/src/overlays/__stories__/TooltipContent.stories.tsx > Default
• Reported colors: foreground #b7b7b8 on background #ffffff (that's gray60 text on white — no green tokens involved)
• Story renders only a TooltipContent with the string "This is the tooltip Content" — no Banner, Card, or wash anywhere
• The same baseline + only different code passed Storybook A11y cleanly on fix: use 8px gap between Alert action buttons #690, and the most recent master run was also green
• 829 of 830 a11y assertions passed here; the new #F0FFF9 ⇄ green60 pair passed its WCAG-AA contrast check

A maintainer re-run of the A11y job from inside coinbase/cds should clear it. Same for the Percy Visreg Web/iOS jobs, which fail because PERCY_TOKEN isn't exposed to fork PRs.

[cb-ekuersch]

we will need to rebase this back onto master