The Selection Color area shows the current colors for visible and hidden nodes, and provides a browse button for each color. To modify either color:
Pale, neutral colors are recommended for backgrounds because they make the difference marker colors easy to see.
To display selection colors properly, you should use a high-color display (more than 256 colors). With 256 or fewer colors, the default selection colors may appear dithered, and it may be difficult to find pleasing alternative colors.