Specify the default symbol and line colors for groups in graphs

File > Options > Graphics > Data View With Groups > Symbol and Line Colors

For graphs that have symbols or lines, each group can be displayed in a different color. Specify the default number and colors of symbols or lines 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 colors, then Minitab repeats the colors.