this night I was thinking of implementing the feature by myself and sending the sources to you.
Of course I prefer the "real" solution, with Color4f background and AlphaBits into GraphicsConfig.
It should not be _that_ complicated and I can implement the feature today itself. Even more I'm sure this feature does not break any backwards compatibility.
I can also implement the ".properties" version if you want, but I could miss the possibility to have offscreen opaque backgrounds when the property is set.
Let me know.