Blender Render: PNG image on semi-transparent colored object I need to put a png image on a semi-transparent cylinder. Like a logo on a colored cup. I need to achieve it only blender render (no cycles, because export in a 3rd party program).

SUM UP :
colored semi-transparent cylinder (like alpha 0.8, color red)
PNG logo with transparent background.
Logo is all around the cylinder, so we have to see the backface.
Logo is opaque
Logo could have several color
I'm not sure to understand what you mean, but I feel you maybe just need to enable this flag in the "shadow" section of the blender internal material settings: "receive transparent".

Here I created a (guess somewhat) similar setup, and without that flag the result is like this



while after enabling it, you can see the "hidden" image behind the semitransparent "glass"



note I here used "raytrace" transparency, but it should work with "Z transparency" too...