Is the idea that Nautilus should draw icons over whatever underlying system is drawing wallpapers (composited desktop container) or that you want to add some transparency to an existing image while applying it.

The former is a duplicate, the latter is a bug in GnomeBG.

Created attachment 139816 [details]
screenshot

I'v attached a screeshot, 
the present dialogue on top > only allows the color to be selected
below is the cairo dock > in addition allows opacity of the color to be set.

Was hoping something like this could be allowed for the nautilus background.
So that the background alone is semi-transparent, while the folders/files are untouched by this setting.

Such an Opacity Setting can be set for either the image or the color selected for the background.

Reassigning to GnomeBG (though picking the color will need to be done from the Appearances caplet, it'll probably need code in both places).

I think you misunderstood me...
This is for the > Backgrounds and Emblems settings
I was suggesting for the nautilus windows not the desktop

Or if this has to be done in GnomeBG ... OK

Per discussion on IRC...

*** This bug has been marked as a duplicate of 444320 ***

i'm a bit confused by that bug! 

i'm not talking about the desktop , 
but rather about the nautilus *file browser* background transparency .

we can currently choose the background color/pattern of the file browser but not the transparency of the background.

That bug seems to be about something different...

that is why i reported this feature in the Component : Backgrounds Emblems and Themes .

I'm not sure both are the same.

Created attachment 139826 [details]
KDE-folder view

KDE allows a single folder , in folder view.[see attachment]

Similar to that, so that all folders have a semi-transparent backgrounds