I think its tricky and the khaki stuff is so bloody cheap anyway its not worth the hassle mate.
I think you'd be better dying grey than blancoing it if you must use it.
"I think we are in rats' alley - Where the dead men lost their bones."
I've done it on an RAF holster. A long soak plus vigorous scrubbing to remove as much of the blue as you can (mine went a pale grey), dry then blanco. The final effect isn't the same as natural webbing + blanco.
But as Gadge says, it's not worth the hassle unless you already have the RAF kit, khaki webbing is cheap even for cheapskates!
I would say keep the RAF Webbing as its already blancoed blue and you cant get blue blanco anymore.
So just get some nice unblancoed webbing then blanco that KG3 instead 