Ummm, so where ever the transparent text is placed, the object "underneath" it along the line of sight should be made transparent? If there are multiple layers then should only the top-most along the line of sight be made transparent or everything all the way through? If there are two objects at equal distance along the line of sight then should they both be made transparent or should only one of them be, paying attention to to sortorder
Now if it is to pay attention to sortorder then notice in Mike's 2D example that outlines can end up being drawn: how should a "one layer exposed only" rule be processed at those edges?
OK, and to confirm, exactly what is made transparent is to vary in real time as the user rotates the scene in three-space?
Would it be acceptable to to simply grab the axes background color and render the font in that? That would typically be an off-white.