How can I select a default color for the Highlight Tool?

There are four standard highlight colors and three custom highlight colors. You can create your custom colors under PDFpen/Pro > Preferences > Editing (Command+comma). When you are ready to highlight, click the Highlight button in the toolbar and select a color, such as one of the custom colors, from the Highlight dropdown menu. The chosen color will remain the default color for that tool unless changed.

To learn more about highlighting and Preferences in PDFpen, please see our Help manual in-product via the Help menu.