Selection Appearance 

When the user selects an item, provide visual feedback so that the user can distinguish the item from those that are not selected. Selection appearance generally depends on the object and the context in which the selection appears.

Display the selection appearance only for the active window or pane. However, in some contexts it might be appropriate to display multiple-selection appearance. For example, when the user selects an object and then selects a menu item to apply to that object, the selection appearance is always displayed for both the object and the menu item to clarify where the user is directing the input. In some cases, you need to show simultaneous selection, but with the secondary selection distinguished from the active selection. In these cases, you can draw an outline in the selection highlight color around the secondary selection or use some similar variant of the standard selection highlight technique.

Highlighting

For many types of objects, you can display the object, its background, or some distinguishing part of the object by using the system highlight foreground and background colors.

The GetSysColor function provides access to the current setting for the system selection highlight color (COLOR_HIGHLIGHTTEXT) and selection background color (COLOR_HIGHLIGHT). Always use these two system colors in their proper foreground and background combination.

In a secondary window, it may be appropriate to display selection highlighting when the highlight is also being used to reflect the setting for a control. For example, in list boxes, highlighting often indicates a current setting. In cases like this, provide an input focus indication as well so the user can distinguish when input is being directed to another control in the window. You can also use check marks instead of highlighting to indicate the setting.

Handles

Handles provide access to operations for an object, but they can also indicate selection for some kinds of objects. The typical handle is a solid, filled square box that appears on the edge of the object.

The handle is hollow when it indicates selection but is not a control point by which the user can manipulate the object.

Base the default size of a handle on the current system settings for resizable window border thickness and on the thickness of the lines in the current system setting for an edge. Then your handles will be sized appropriately to be visible, and will be easily targeted with the mouse when the user changes window border widths or resolutions. Similarly, the colors you use to draw handles should be based on system color metrics so that when the user changes the default system colors, handles change appropriately.

The system settings for window border and edge metrics can be accessed by using the GetSystemMetrics function.

When you use a handle to indicate selection, display the handle in the system highlight color. To help distinguish the handle from the variable background, draw a border around the edge of the handle by using the system's setting for highlighted text. For hollow handles, use the opposite: the selection highlight color for the border and the highlighted text color for the fill color. If you display handles for an object even when it is not selected, display the handles in a different color, such as the window text color, so that the user does not confuse it as part of the active selection.