public int getPreviewColor() {
        return previewChartRenderer.getPreviewColor();
    }
Preview chart that can be used as overview for other ColumnChart. When you change Viewport of this chart, visible
area of other chart will change. For that you need also to use
{@link Chart#setViewportChangeListener(lecho.lib.hellocharts.listener.ViewportChangeListener)}

@author Leszek Wach
hellocharts-library/src/lecho/lib/hellocharts/view/PreviewColumnChartView.java