Remind me which camera you have? When in review mode after a still shot, try hitting the up or down arrow on the multi-selector button (the one with "okay" in the middle)
There are no zebra highlights during still live view, only during movie live view. You can bring up a histogram (next best thing) during still live view with the "info" button.
Comments
in the review mode it works, but in movie mode it is there in real-time, not only after taking the shot.