Thanks for the answer. I was hoping for something a bit less interactive. LR lets me just hover over a button so see anything at 0 or 255, or I can activate the upper and/or lower button to leave the clipping display on. Very much like a camera viewfinder. Even better would be something like a clipping option on the view menu. It's a way to make a quick check when doing blends.
Hi,
As an alternative you can add a Threshold layer as the top layer, especially useful when doing multi-layer blends, and by sliding the cut-off point to the shadows or the highlights you can see where the clipping takes place. Granted, not very elegant, but it does the job and works with blends.
Cheers,
Bart