Using the RadPieChart and PieSeries (UI for Xamarin v2019.2.802.1 from NuGet), I can currently set the LabelBinding (or LabelFormat or LabelFormatter) to adjust the strings displayed in the labels on the slices of the pie chart, but unlike other chart controls, I currently have no way to modify the styling of those labels like I can in every other chart control I've used from Telerik UI for Xamarin.
It seems to me that it would be best to have more properties on the PieSeries class, like LabelFontSize, LabelFontAttributes, LabelFontFamily, LabelTextColor, and LabelMargin (Label prefix to distinguish from LegendTitleBinding could be kept or discarded as desired on some of these names).
LabelMargin would be particularly helpful to eliminate the UWP situation wherein currently all pie slice labels overlap with the outer lighter ring of the pie chart (see image from UWP). The others just seem needed to maintain a consistent appearance of charts within an app - if all my chart labels are dark blue and a different font size and style except for the not-style-able black labels in pie charts, that makes pie charts hard to incorporate without looking bad or forcing styling elsewhere to match the pie charts' fixed values.