Click the Stage Color swatch and select a dark gray (#333333) or black.

If you must use Flash CS6 for legacy projects, consider these external solutions to help with the light UI:

Since you cannot change the global UI color with a single switch, follow these steps to darken the most visually prominent areas:

This only changes the background for the current project. To make it permanent for all new files, select "Make Default" in the Document Settings dialog. 2. Customize the Pasteboard (Work Area)

Change the Background color to dark gray or black. You will also need to adjust the Syntax Coloring (text colors) to lighter shades (e.g., white or lime green) so the code remains readable on the new dark background. Comparison: Flash CS6 vs. Modern Alternatives