Presentation graphics matches the color pool with a collection of different line styles called the “style pool.” Entries in the style pool define the appearance of lines such as axes and grids. Lines can be solid, dotted, dashed, or some combination of styles.
The second member of a palette structure defines a style code as
unsigned short style;
Each palette contains a style code that refers to an entry in the style pool in the same way that it contains a color code that refers to an entry in the color pool. The style code value in a palette is applicable only to line graphs and lined scatter diagrams. The style code determines the appearance of the lines drawn between points.
Summary: Use the different line styles in the style pool to differentiate series.
The palette's style code adds further variety to the lines of a multiseries graph. It is most useful when the number of lines in a chart exceeds the number of available colors. For example, a graph of nine different data series must repeat colors if only three foreground colors are available for the display. However, the style code for each color repetition will be different, ensuring that none of the lines looks the same.