SUMMARY
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Right now Kalendar seems to sync with your calendar services of choice just fine. But it cannot pick up on the colour you chose to use for different event types. Like if you setup doctor appointments to use one colour, and meetings to use another via the first party client for your calendar service of choice. Like the Apple Calendar or Google Calendar service, using their respective first party apps for example. Kalendar will not pick up on that colour choice. It would be nice if it could. In the same vein, it would be nice if Kalendar used the colours that services like Apple and Google Calendar used. So that when you setup an event in the Kalendar application, the colour you choose for that event would also be able to be shown in Google/Apple Calendar for example. Or whatever other calendar service you chose to use for that matter. Maybe Kalendar could only show you colour options that were compatible with the calendar service that you are currently using as well. That way you know your calendar events will display their colour correctly when using the first party client provided by your calendar service to view your calendar. Like the Google Calendar or Apple Calendar mobile apps for example.
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Issue: 
Colours used in Kalendar do not appear to be compatible with the calendar service that the Kalendar app is currently hosting. Also Kalendar seems to be unable to pickup on the colour that you set for different events in your calendar service's native application.


EXPECTED RESULT
For Kalendar to at least be able to pick up on the colour you set for certain events within your calendar service's native application. And one better if this is even possible, if Kalendar offered you colour choices that the calendar service that is currently being hosted by Kalendar would be ok with. (I can see how this second thing could be a little difficult to pull of though, depending on how much the backends of different calendar services allow you to do via 3rd part calendar clients like Kalendar.)

SOFTWARE/OS VERSIONS
Linux/KDE Plasma: 
Distro: openSUSE Tumbleweed (20220923)
KDE Plasma Version: 5.25.5
KDE Frameworks Version: 5.98.0
Qt Version: 5.15.5

ADDITIONAL INFORMATION
I would just like to apologize in advance if you can already do some of the things I mentioned here and I just happened to not know about them, and/or how to get them working. That seems to happen way too often when I post bugs/feature suggestions.