Outlook's dark mode for Android is fine.  According to Windows Central, the iOS version will look about the same when it is released. Microsoft is working to speed up the work of smartphones, because Outlook for Windows 10, Outlook on the Internet, Windows 10 email client and Office have long been included in a dark theme. It is not clear when Microsoft will update Outlook for Android and iOS with a dark mode, but, given the screenshot, most likely it will happen soon.

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In its latest release, Outlook for iOS supports color categories in the calendar when it comes to updates. Users need to set the category color in their Office 365 account so they appear in the iOS app.

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Both Google and Apple are building system-wide dark modes in Android and iOS this year, as well as the API that will allow developers to tap into the system theme and set up their app automatically for whatever the user has set up for the system. Perhaps Microsoft is waiting for both Android and iOS to officially support Dark mode before applying Dark Mode in Outlook, which explains why it has taken so long to look like that.