[Tex/LaTex] How to set opacity/transparency to vector image


Hold your horses!. If you are hurrying to flag this as a duplicate of
this question or this question none of those have an answer
to what is asked here. Thanks for the attention though.

I have an .eps image (the idea is to keep this image and don't change it's format to a .png for example), that I am setting as background for a project with the background package:

contents={\tikz[remember picture,overlay,shift=(current page.center)] \node[inner sep=0pt] at (8,-10){\includegraphics[scale=1]{Cube.eps}};}}

The original image is (have it here with black background):

And the result setting the opacity in both the background setup and tikz node options is the following:


I created the image with InkScape and I actually set the "color layers" as unmasked by the opacity command in order to make the color gradient. Obviously this is not the desired result, what is expected is something like:


Is this posible?.