Transparent LibGDX in transparent jFrame not rendering properly

Question

I created a transparent LibGDX canvas in a custom JFrame (https://stackoverflow.com/a/21258666/4941895). The problem now is that when I render anything it all looks semi transparent like the color black was totally missing out. Here is a screenshot:

http://www.upload.ee/image/4744693/2015-05-25-071437_1920x1080_scrot.png

In my render loop i call:

Gdx.gl.glClearColor( 0, 0, 0, 0);
Gdx.gl.glClear( GL20.GL_COLOR_BUFFER_BIT | GL20.GL_DEPTH_BUFFER_BIT );

And this is the section I use to make my frame transparent:

theFrame.setUndecorated(true); 
theFrame.setBackground(new Color(1.0f,1.0f,1.0f,0.1f));

So how could things be displayed normally on a transparent frame?