foreach (FloatingChartShape chart in wsPureCompTemplate.Charts)
{
    foreach (SeriesGroup seriesGroup in chart.Chart.SeriesGroups)
    {
        foreach (SeriesBase series in seriesGroup.Series)
        {
            LineSeries lineSeries = series as LineSeries;
            if (lineSeries != null && lineSeries.Marker != null && lineSeries.Marker.Fill == null)
            {
                lineSeries.Marker.Fill = new NoFill();
            }

            ScatterSeries scatterSeries = series as ScatterSeries;
            if (scatterSeries != null && scatterSeries.Marker != null && scatterSeries.Marker.Fill == null)
            {
                scatterSeries.Marker.Fill = new NoFill();
            }
        }
    }
}