Select the Draw Behind box to draw or color behind the lines of that layer (left) and the onion skinning buttons and options.

I have found the onion skinning to be very helpful. Click one button to turn the onion skin on or off and you can set it to view anywhere from 0-3 panels behind and another 0-3 panels in front of your current panel.

While you're working, you can quickly view large portions of your board on one screen. This is helpful while developing sequences and conferring with directors. You may also view your boards in the classic horizontal and vertical workspaces. You can also draw directly in the frames while in these views.

It is possible to import audio files in .WAV, .AIF and .MP3 formats while in the timeline workspace. You can split the audio file at any frame for editing.

Panel with onion skin turned on (top) and overview workspace.