<c1chart:ChartView.AxisX>
      <c1chart:Axis>
        <c1chart:Axis.Resources >
          <local:ColorConverter x:Key="clrcnv" />
        </c1chart:Axis.Resources>
        <c1chart:Axis.AnnoTemplate>
          <DataTemplate>
            <TextBlock Width="25" TextAlignment="Center"
             Text="{Binding Path=Value}"
             Foreground="{Binding Converter={StaticResource clrcnv}}"/>
          </DataTemplate>
        </c1chart:Axis.AnnoTemplate>
      </c1chart:Axis>
    </c1chart:ChartView.AxisX>

public class ColorConverter : IValueConverter {
   int cnt = 0;
   public object Convert(object value, Type targetType,
     object parameter, CultureInfo culture)
   {
     //DataPoint dpt = (DataPoint)value;
     // ブラシを交互に切り替え
     return cnt++ % 2 == 0 ? Brushes.Blue : Brushes.Red;
   }
 
   public object ConvertBack(object value, Type targetType,
    object parameter, CultureInfo culture)
   {
     return null;
   }
}