Apple Final Cut Pro 7 - Manual (Page 1162)

If you make a clip play backward by selecting the Reverse checkbox in the Change Speed
dialogs, the speed indicators turn red to show that playback is going backward in time.
Reverse-speed indicators
are red.
When you make variable speed changes, the duration of the affected clip stays the same.
The Timeline speed indicators display all speed changes—fast-forward, slow motion, and
reverse—happening within the clip. In particular, because variable speed changes can
also transition smoothly from one speed to another, the spacing of the speed indicators
indicates the acceleration of the speed change.
1162 Chapter 69 Changing Clip Speed