Hi Emil,
Thank you for your interest in Syncfusion products.
As of now, the mentioned support to customize the Schedule MonthView Appointment indicator is not available in Xamarin Forms. We have considered to implement this feature for customizing the Appointment Indicator color and customizing the entire notation UI. We have logged feature report for the same, we will implement and include this feature in any of our upcoming Volume release.
Regards,
Subburaj Pandian V.