With Windows XP, Windows themes were introduced. Windows themes can be selected by the user using the Control Panel. If a theme is selected, the display of user interface controls adapts to the current display theme. Themes can provide various display styles for the same control. With themes active, Windows renders (paints) the control.
By using the UseThemes property, controls can adapt to the current theme used. If set to False, themes are not honored and the controls are rendered using the built-in style. This makes it easy to use the same application across all supported platforms. If Windows themes are not available, the control will simply use its built-in display style, otherwise it will fully exploit Windows themes.
To prepare an application for proper themes support, the control should be designed and tested under Windows XP or Windows Vista. It should be viewed both with and without themes to make sure that the defined control is visually satisfactory in both cases. Controls designed for use on Windows XP or Windows Vista with themes will work identically on all other platforms, even when themes support is not available.
Keep in mind that numerous control definitions, particularly relating to colors,
have no effect when themes are active. You can find out if a specific control
setting has any effect with themes active by consulting the detail information
in this documentation.