In Support Forum, I've posted a comment which tells people how to create a userChrome.css file and use specific code to force the category colour to be applied across the the top. For those needing a workaround in the interim please use this link: https://support.mozilla.org/en-US/questions/1368838#answer-1493441
Bug 1674896 Comment 16 Edit History
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In Support Forum, I've posted a comment which tells people how to create a userChrome.css file and use specific code to force the category colour to be applied across the the top. This applies to version 91* For those needing a workaround in the interim please use this link: https://support.mozilla.org/en-US/questions/1368838#answer-1493441