this isn't a feature of the chart, but you can make it happen using code like this:

        private void XamWebChart_DataItemMouseEnter(object sender, Infragistics.Silverlight.Chart.DataItemMouseEventArgs e)
        {
            Path wedgePath = e.Element as Path;
            if (wedgePath != null)
            {
                ColorAnimation yellowAnimation = new ColorAnimation();
                yellowAnimation.From = Colors.Yellow;
                yellowAnimation.Duration = TimeSpan.FromSeconds(1);
                Storyboard glow = new Storyboard();
                glow.Children.Add(yellowAnimation);
                Storyboard.SetTarget(yellowAnimation, wedgePath.Fill);
                Storyboard.SetTargetProperty(yellowAnimation, new PropertyPath("Color"));
                glow.Begin();
            }
        }

        <igChart:XamWebChart DataItemMouseEnter="XamWebChart_DataItemMouseEnter">
            <igChart:XamWebChart.Series>
                <igChart:Series ChartType="Pie">
                    <igChart:Series.DataPoints>
                        <igChart:DataPoint Value="1" Fill="Red" />
                        <igChart:DataPoint Value="1" Fill="Green" />
                        <igChart:DataPoint Value="1" Fill="Blue" />
                    </igChart:Series.DataPoints>
                </igChart:Series>
            </igChart:XamWebChart.Series>
        </igChart:XamWebChart>