There are two color coding modes.
Automatic color coding
When choosing automatic color coding, each unique values in the chosen column will be assigned a unique value. Consider the following SharePoint list.
Please note, Automatic color coding regenerates a random color for each unique value every time the graph loads. When saving a graph, the color assigned is NOT saved. Random color is generated each time.
For more fine control of coloring, try manual color coding.
Manual color coding
Manual color coding allows you to specify a unique color to items. Consider the following example:
In the above example, all items which satisfy this condition “Organisation = “My organisation”” will be assigned blue color.