Which option is selected to apply a Colored Outline in a diagram's styles?

Applying a Colored Outline to a diagram's styles typically involves using features found in the Format Ribbon Tab. This tab is specifically designed for formatting shapes, including their outlines, fill colors, and various styles. Within the Format Ribbon Tab, users can access options to modify the appearance of shapes and diagrams. This includes setting the color and style of outlines, which is essential for enhancing the visual appearance and making elements distinguishable in presentations or documents.

The Shape Styles Gallery and SmartArt Styles provide predefined sets of styles and layouts for shapes and SmartArt graphics, respectively, but these options do not directly allow for the customization of outlines like the Format Ribbon Tab does. The Design Ribbon Tab focuses more on layout and design elements for broader content arrangements rather than the specific formatting of individual shapes within a diagram. Thus, the most suitable option for applying a Colored Outline aligns with the capabilities provided in the Format Ribbon Tab.