I'm a little confused as to what control you're referring to. You've submitted this under the RadCalendar, for which you can indeed create a custom renderer, see this documentation
You also mention the Chart, here's the documentation
on how to create a renderer for the Chart.
Lastly, you'll want the native component's documentation in order to know which properties are available to you in the custom renderer. Here are the links:
The native component documentation has code tabs that lets you switch to C# so you can see the approaches for Xamarin implementation.
Lance | Tech Support Engineer, Sr.
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