ofxsimpleguitoo with transparency ?

I admit I haven’t looked too much into solving this…

I would like to render the gui with a transparency so that you can see what’s behing the UI (which I think it’s something quite of a common problem if you have the UI overlaying your project).

Some stupid colour setting with the alpha

  
  
ofSetColor(255,255,255,100);  
  

is not working… any ideas (possibly without interfering with ofxsimpleguitoo files) ?

Thanks!