Hi @Alan Bradbury,
Based on your description, I can provide you with the following suggestions for your reference:
- You can try to clear the browser cache and make sure that Microsoft Edge is the latest version.
- Please check whether the theme-color value of the name attribute in the HTML <meta> element is used, which may override the specified theme colors in the manifest file.
- Please check whether the preference for light or dark mode is set in Edge, which may also adjust the applied theme color based on user preferences. If a user has set a preference for light or dark mode, Edge may override the manifest theme color value to support any prefers-color-scheme media query defined in the app's CSS.
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Best Regards,
Jinxin Wang