Hello Tiago, 

Thank you for contacting Infragistics. The RingSeries allows for the label colors to be changed based LabelInnerColor and LabelOuterColor. However if you want to make further customizations, like changing the text, it will be limited by the FormatLabel event. This event exposes the Label and the Item. I tried this out but you cannot style the font or font size out of the box through the event args.

eg.

public partial class MainPage : ContentPage
    {
        public MainPage()
        {
            InitializeComponent();
        }

        private void ringSeries_FormatLabel(object sender, Infragistics.XamarinForms.Controls.Charts.PieChartFormatLabelEventArgs args)
        {
            var item = args.Item;
            if (item.Item.GetType() == typeof(FinancialDataPoint))
            {
                var finItem = (FinancialDataPoint)item.Item;
                if (finItem != null)
                    args.Label = finItem.Spending.ToString();
            }
           
        }
    }

    public class FinancialDataCollection : ObservableCollection<FinancialDataPoint>
    {
        public FinancialDataCollection()
        {
            this.Add(new FinancialDataPoint { Spending = 20, Budget = 60, Label = "Administration" });
            this.Add(new FinancialDataPoint { Spending = 80, Budget = 40, Label = "Sales" });
            this.Add(new FinancialDataPoint { Spending = 30, Budget = 60, Label = "IT" });
            this.Add(new FinancialDataPoint { Spending = 80, Budget = 40, Label = "Marketing" });
            this.Add(new FinancialDataPoint { Spending = 40, Budget = 60, Label = "Development" });
            this.Add(new FinancialDataPoint { Spending = 60, Budget = 20, Label = "CustomerSupport" });
        }

    }
    public class FinancialDataPoint
    {
        public string Label { get; set; }
        public double Spending { get; set; }
        public double Budget { get; set; }
    }

I suggest submitting a new product idea. 

You can suggest new product ideas for future versions (or vote for existing ones) at <https://www.infragistics.com/community/ideas>.
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