matteColor - do not work

[baldo]

I wanna save a GIF, trasparent, with matte color...
with this part of code I've got no MATTE...

tnxS!!

saveOptions = new ExportOptionsSaveForWeb();
saveOptions.format = SaveDocumentType.COMPUSERVEGIF;
saveOptions.colorReduction = ColorReductionType.SELECTIVE;
saveOptions.colors = 128;

saveOptions.matteColor = Rgbcolor.red(236);
saveOptions.lossy = 0;
saveOptions.dither = Dither.NONE;
saveOptions.optimized = true;
fileimmagine.exportDocument(saveFile, ExportType.SAVEFORWEB, saveOptions);