Tertiary color does not have correct Color Contrast ratio.

[dhoehna]

Describe the bug

The tertiary color brush does not have the correct CC ratio.

Steps to reproduce the bug

1. Open up the WinUI 3 Gallery
2. Go to Design Guidance -> Colors
3. Open accessibility Insights for Windows.
4. In the accessibility insights, go to the Color Contrast Analyzer.
5. Turn on Auto-detect contrast ratios.
6. Hover over the tertiary text in the WinUI 3 Gallery.

Expected behavior

The CC ratio is over 4.0

Screenshots

NuGet package version

WinUI 3 - Windows App SDK 1.5.3: 1.5.240428000

Windows version

Windows Insider Build (xxxxx)

Additional context

No response

[github-actions]

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