Control developers use the System.Web.UI.ThemeableAttribute attribute to decorate control types and their members, to signal which ones can and cannot be affected by themes and control skins. By default, all properties exposed by a control are themeable. However, themes are typically applied only to stylistic properties; the Themeable(false) attribute should be applied explicitly to all non-stylistic properties. Decorating a member with the Themeable(false) attribute ensures that the member is not themed, regardless of the value of the Control.EnableTheming property. For example, if the System.Web.UI.ThemeableAttribute attribute is applied to a control and set to false, the control is not affected by themes even when its Control.EnableTheming property is set to true.

The System.Web.UI.ThemeableAttribute class maintains a static list of all types that support themes, and this list is consulted whenever the static methods ThemeableAttribute.IsObjectThemeable(object) and ThemeableAttribute.IsTypeThemeable(Type) are called.