When set to a color other than Color.Transparent (the default), all occurrences of the color in the image will be made transparent.
If an image is supplied by setting an Appearance.Image property to an Imagelist index, the ImageLists TransparentColor property is looked at first. If the property is set to Color.TransparentColor, then the control's ImageTransparentColor is used. If it is set to Color.TransparentColor, then no color masking is done.
If an image is supplied by setting the Appearance.Image property to an image, the control's ImageTransparentColor is used. If it is set to Color.TransparentColor, then no color masking is done.
Target Platforms: Windows 10, Windows 8.1, Windows 8, Windows 7, Windows Server 2012, Windows 7, Windows Vista SP1 or later, Windows XP SP3, Windows Server 2008 (Server Core not supported), Windows Server 2008 R2 (Server Core supported with SP1 or later), Windows Server 2003 SP2