Which variety mojo? The prime-time coloring and skin condition vary from variety to variety. Black Beauty sins will be uniformly dark (no green) and very shinny. Ichiban may have a small amount of white-green around the very top. See pics of ripe ones linked below.

You can learn much more about growing and picking them over on the Vegetable gardening forum here too.

Dave

Here is a link that might be useful: Pictures of ripe eggplants

What I've learned is to pick them BEFORE they lose the shiny, dull is too old. Can still be used, but not as good. Size doesn't matter as much. After awhile, you'll figure what stage you like them at.