When a new run is created, it is assigned a default color. You can edit the color for a given run by clicking the color preview.
Colors are locally scoped. On the project page, custom colors only apply to your own workspace. In reports, custom colors for runs only apply at the section level. You can visualize the same run in different sections, and it can have a different custom color in each section.
Select the Run you want to visualize
Click the colored dot
Select a color for the graphs of your run