You can change the appearance of the charts like Foreground, Background, Border etc. Check out the sample below to discover what is possible.
<chart:ClusteredColumnChart ChartTitle="Column Chart" ChartSubTitle="Chart with fixed width and height" ... Width="450" Height="450" BorderBrush="Black" BorderThickness="2" Foreground="Blue" Background="LightBlue" FontSize="12" SelectedBrush="Yellow" > <chart:ClusteredColumnChart.Series> ... </chart:ClusteredColumnChart.Series> </chart:ClusteredColumnChart>
Result