This is perhaps a little late for the OP but for anyone else trying to solve these problems I hope it helps...

Hiding label text on the pie chart

To hide label text on the pie chart without affecting the legend you can simply set the foreground colour of the pie chart to "Transparent" and set the label position to any value other than "None".

An example style is shown here:

    <Style TargetType="ig:XamPieChart"
           x:Key="PieChartStyle">
 
        <Setter Property="LabelsPosition"
                Value="Center" />
 
        <!-- This is to prevent the label values from appearing on the chart slices-->
        <Setter Property="Foreground"
                Value="Transparent" />         
 
    </Style>   

Interpolating chart colours

The WPF DV XamChart control has StartPaletteBrush and EndPaletteBrush properties for this purpose. In the Silverlight control it is necessary to roll our own. The best method I have found is to create a ValueConverter that has two public properties - one for the start colour, and one for the end colour. It should accept an integer parameter which represents the number of slices on the chart. It then returns a BrushCollection object containing the colours which are calculated using linear RGB interpolation. Set the Brushes property of the XamPieChart to a binding that uses this converter and give the number of slices as the converter parameter. This works for me because I know how many items my chart is displaying. The classes involved are shown below:

    public class ColorsToBrushCollectionConverter : IValueConverter
    {
        public Color StartColour { get; set; }
        public Color EndColour { get; set; }
 
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            if (value.GetType() != typeof(int))
                return DependencyProperty.UnsetValue;
 
            int steps = (int) value;
 
            BrushCollection brushes = new BrushCollection();
 
            ColorInterpolator.InterpolateColours(StartColour, EndColour, steps).ToList().ForEach(c => brushes.Add(new SolidColorBrush(c)));
            
            return brushes;
        }
 
        public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            throw new NotImplementedException();
        }
    }   

    public static class ColorInterpolator
    {
        public static Color[] InterpolateColours(Color startColour, Color endColour, int steps)
        {
            Color[] colours = new Color[steps];
            double s = (double) steps;
 
            double aDelta = (endColour.A - startColour.A) / s;
            double rDelta = (endColour.R - startColour.R) / s;
            double gDelta = (endColour.G - startColour.G) / s;
            double bDelta = (endColour.B - startColour.B) / s;
 
            for (int i = 0; i < steps; i++)
            {
                Color c = Color.FromArgb(
                    (byte) (startColour.A + (i * aDelta)),                    
                    (byte) (startColour.R + (i * rDelta)),
                    (byte) (startColour.G + (i * gDelta)),
                    (byte) (startColour.B + (i * bDelta)));
 
                colours[i] = c;
            }
 
            return colours;
        }
 
    }