Outline

Outline Tool

Shortcut Key:- F

You can use the Outline command to fill outline to the color patch.  paint a colored border around a selection or similar color. You can also define the size of outline from Brush width.

Left click fills primary color outline outside the pattern

Right click fills secondary color outline outside the pattern

+ Hold Ctrl and left click will fill primary color outline inside the pattern.

+ Hold Ctrl and right click will fill secondary color outline inside the pattern.

+ Hold Shift and left click to draw outline for all similar colors in design.

Original design(left), left clicked to outline(middle), Shift + left clicked to outline all similar colors in design(right)

Button makes outline thicker and   button makes outline thinner or  use Brush Width option to select the thickness of the outline.