Apple Final Cut Pro 5 - Manual (Page 1167)

380 Part II Project Interchange
 Alpha+RGB: This option lets you see a representation of the alpha channel overlaid
on top of the RGB channels that constitute the actual image of the video clip. The
alpha channel is overlaid in red, with solid red representing nontransparent areas.
The RGB and Alpha options in the View menu are most effective when used with
different backgrounds (described in the next section).
Choosing a Background
When working with clips that have an alpha channel, you can choose different
backgrounds that make it easier to see which areas of your picture are transparent.
Translucent clips or generated text may be easier to see if you choose a background
that emphasizes them, such as Checkerboard 1 or 2. If you’re compositing colored
images, a contrasting color would work better.
When a clip is rendered for export to tape, the background is always set to black. If it is
rendered for export as a QuickTime movie, the background will still appear to be black,
even if the alpha channel is exported along with it.