I know max has one, z brush has a ghosting mode which makes everything other than the mesh you are working on transparent which is not helpfull, especialy w/ orthographs. Either that Or ive got a wrong setting somewhere.
I'm not quite sure the effect you're trying to achieve. If you want transparency/ghosting to affect the selected subtool, you can adjust the opacity settings under Preferences: Draw If you're looking make the mesh transparent for the sake of working with orthographic reference, you could consider the image plane option…