TFlexCelHtmlExport.FixIE6TransparentPngSupport Property
By default, Internet explorer does not support transparent PNGs. Normally this is not an issue, since Excel uses little transparency. But if you rely on transparent images and don't want to use gif images instead of png, you can set this property to true. It will add special code to the HTML file to support transparent images in IE6. Note: If setting this property to false, you might want to set ImageBackground to Colors.White instead of TUIColor.Empty to ensure images have no transparent background.
Syntax
Unit: FlexCel.Render
property TFlexCelHtmlExport.FixIE6TransparentPngSupport: Boolean