( resource image [, int color] )
imagecolortransparent() sets the transparent
color in the image image to
color. image is the
image identifier returned by imagecreatetruecolor() and
color is a color identifier returned by
The transparent color is a property of the image, transparency is not a
property of the color. Once you have set a color to be the transparent
color, any regions of the image in that color that were drawn previously
will be transparent.
The identifier of the new (or current, if none is specified)
transparent color is returned.