From Xojo Documentation
The currently selected color for outlining objects, as set by the operating system.
|result||Color||The color used for drawing the outline of a RectControl.|
This value is useful when you are using Canvas controls to create custom controls. When drawing objects, use this color for the object's frame. ListBoxes, for example, use this color to draw the dark frame around the ListBox.
This value can be changed by the user, so you should access this value in your Paint Event handler rather than storing the value.