There is also an issue in current version 91.3.2 If computer High Contrast Black selected: The top toolbars, Folder Pane, Thread Pane and Message Pane header area, Write window effected - only drop down menu seems ok. Calendar, Task and Events, Today Pane all effected. They show the same colours determined by the Light or Dark theme in Thunderbird and not the High Contrast Black theme. The Language and Appearance 'Colours' section is setup to use 'Only with High Contrast themes'. I'll create a separate bug if required, but support forum has reported this.
Bug 1731453 Comment 1 Edit History
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There is also an issue in current version 91.3.2 If computer High Contrast Black selected: The top toolbars, Folder Pane, Thread Pane and Message Pane header area, Write window effected - only drop down menu seems ok. Calendar, Task and Events, Today Pane all effected. They show the same colours determined by the Light or Dark theme in Thunderbird and not the High Contrast Black theme. The Language and Appearance 'Colours' section is setup to use 'Only with High Contrast themes'. I'll create a separate bug if required, but support forum has reported this. Visibilty is seriously effected; I think this needs more priority.