Hello,
Thanks for the quick answer.
:) yes green with green was not a good example.
It seams that is a common question over the web. i found the comment bellow and i think maybe the problem is the images that i use, but i need to make a few tests.
"Only certain graphic file formats offer transparency as an option. One example is the GIF format.
Although some scanning software can produce a GIF, none that I know of automatically remove the white background to produce transparency.
In other words, just because you have a GIF file doesn't’t mean it has transparency.
You’ll need to use a tool to remove the background to produce the transparent effect."
From :
http://www.gregledet.net/?p=5