Specify the default fill colors for groups in graphs

File > Options > Graphics > Data View With Groups > Fill Colors

For graphs that have areas, bars, boxes, or pie slices, you can assign a different fill color to each group. Specify the default number and types of fill colors that are available. The changes you make to the defaults remain until you change them again, even after you exit Minitab.

If the number of groups in the data is higher than the number of available fill colors, then Minitab repeats the colors.