Hello~
An easy and fast way to do this is to enable Transparency in the render palette and then go to the subtool palette and you know how there’s those 5 little icons right to the little preview of your subtool? Those are for boolean ops and for visibility.
The third one from the left (like, left of the brush icon) activates transparency of the selected subtool (but only in BPR!)
So hit that Shift+R and see how it works for you.
To adjust the transparency, go to Render -> Bpr Transparency.
Bunch of sliders, play around, enjoy.
There’s certainly better, easier or more effective ways,
but this is what came to my mind. If you wanted to know more, maybe check the Z4 beta threads, there’s some that explore and explain new features such as bpr transparency.
Little tip, ZBrush has that incredibly awesome on the fly help feature going on, if you hold down ctrl while your mouse is over some menu item, it will display a little tooltip to help you figure out what it is and what it does.
It doesn’t work for every object of the interface, but for many.
And if all else fails, you got google and the friendly folks over at pixolator.com.