Transparent game window [Duplicate post]

Dear developers,

Although I understand Unity3D isn't strictly meant for the following feature, I am taking a shot anyhow.
I've been wondering if it is possible to grab a key color and replace all colors with transparency.
This way it should be possible to blend a game client with the operation system.

So let's assume some things:
Windows and possibly Linux.
May need to use C++.
May need to use OpenGL.

Things for sure:
On Windows this is possible with OpenGL and certain API calls.

Thing I am asking:
Is there a feature inside the core Unity which allows for transparency for the entire application? I am not talking about transparent textures or models. I am talking about an actual game being transparent showing the window/screen below the game.

So, could it be done in Unity3D or will it be a very difficult ride to make?

PS: From my searching results there are stand-alone solutions but obviously they do not allow big computations graphically like Unity does. Either that or they won't port to at least Linux.

Thank you for your patience and hopefully contribution the the issue.

 

Thank you for your answer. I was not able to find this post even after searching. I can appreciate that you've shared this discussion with me. Although I am searching for a more cross-platform solution, I believe this particular issue cannot be solved cross-platform. I was making a long shot. In fact, it seems that making transparency in apps is a difficulty on all platforms. I'll give the 'solutions' provided in the thread a try!