When a chart contains only one series and several categories, then by default individual chart segments may use the same fill color (such as individual columns in a column chart) or varying colors (such as segments in a pie chart), depending upon the chart type you are working with. If your chart uses the same colored series in all of the categories, it can make your chart look dull — it also does not provide a proper way for your audience to compare the individual series’ elements.
Learn how you can change the color of category elements (series) in a chart.

