profile.transparency

[Cubical]

I'm trying to make a fade effect but I cannot figure out how to make a GuiControl's transparency to be 0.5. Could someone explain this to me?

PHP Code:

new GuiControl("TestGuiControl_Container"){
  useownprofile = true;
  profile.transparency = 0.5;
  profile.opaque = true;
  profile.fillcolor = {255,255,255,255};
  profile.border = 1;
  x = y = 40;
  extent = "400 400";
}