Hi Matthias,
Thanks for your reply.
If you look at gnome-looks icons, there are lot of icon themes based on a preferred geometry (like circular, rounded-square etc. I personally use https://github.com/numixproject/numix-icon-theme-circle).
As any themed icons-sets, those icons only work with prebuilt icons (those provided by the upstream). If I use a software that is not themed by the upstream, it looks out of place. I have added my screen-shot for an example, with nedit  not themed (see http://picpaste.com/Screenshot_from_2015-05-05_13-34-03-cZkzdwST.png )
In android system, it is very common that if icons are unthemed, then it will get a layer (masking) ...so all icons have same shape.

> Subject: Re: icon-masking in gnome
> From: mclasen@redhat.com
> To: desktop@lists.fedoraproject.org
> Date: Mon, 4 May 2015 10:02:48 -0400
> CC: desktop-devel-list@gnome.org
> On Sat, 2015-05-02 at 19:46 +0100, Rudra Banerjee wrote:
> > Hi,
> > I am a longtime fedora and gnome enduser.
> > I want to propose icon masking facility for unthemed desktop icon, as
> > it is very common in android.
> >
> > I talked to such a icon developer (Numix) and I was told that this is
> > not supported in linux.
> > Is there any work on this?
> > Regards,
> > RudraB
> Could you explain what you mean by icon masking, and why it would be
> useful to have ?
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