first of all, thank for answer...but also how you say: nothing!
2) In Play mode: enter to <Alt> mode and half-press the shutter button. If keyboard mask is correct it will prevent the camera to switch to rec mode. In this case the zebra could be shown.
I see histogram but nothing else => for this, keyboard mask should to be right

Histogram condition:
conf.show_histo && (gui_mode==GUI_MODE_NONE || gui_mode==GUI_MODE_ALT) [...]
I'm not understending...but the IF condition is:
Zebra condition:
conf.zebra_draw && [color=red]gui_mode==GUI_MODE_NONE[/color] && kbd_is_key_pressed(KEY_SHOOT_HALF) && mode_photo
this mean that only view zebra in GUI_MODE_NONE...and not in GUI_MODE_ALT
sorry, this is not important, it's only to learn something

I'm sure there is zebra mode in MODE_PLAY also for this code in gui_osd_draw_zebra():
img_buf=((mode_get()&MODE_MASK) == MODE_PLAY)?[color=red]vid_get_viewport_fb_d()[/color]:vid_get_viewport_fb();
vid_get_viewport_fb_d() should be viewport buffer in MODE_PLAY...
thank...for all support and this fantastic CHDK!!