Turn off the layer's visibility by clicking on the eyeball icon.
Thanks for your reply !
I just want to keep on my comp the frames that I already have on the sequence and get just a black color on the missing frames. I have a 2750 frames sequence and some frames are not ready yet so I get the color - bar and go trough the sequence and add a black solid or key-frames the opacity don't make any sense and is very time consuming on such a long sequence. The missing color - bar is always being very useful but sometimes is not.
Is there a way ?. Maybe a feature in next versions of Ae ?
Just turn off layer visibility or find the missing layer and replace it with a black solid. Turning off the layer visibility does reveal the layer below, but if there was none then you would get black or transparent.