You can change the color of any graph component by using the Color button on the Graph Toolbar.
Select the component.
From the Graph Toolbar, click the Color button.
Choose a color for the selected component.
Note: When you change the color of a particular data marker, then all of the data markers of that same series change to match. When you change the color of a data marker in the plot area, then its corresponding legend marker in the legend area changes to match as well. Similarly, when you change the color of a legend marker in the legend area, its corresponding data marker in the plot area changes to match.