Using color in charts – tool or frill?
Color not only brands the charts to your company's template and color scheme, it is also a powerful tool that should not be traded away unnecessarily. For example, color can be added to highlight segments within a data-driven chart so you can add another layer of information. If the segments are given their own color, therefore, you have traded away this capability for the sake of variety - not a good trade. Keep segments in charts the same color so that you have options if you need them. Rely on the lines to make the separations between the segments instead of colors.