Apple Final Cut Pro 6 - Manual (Page 1201)

416 Part II Effects
 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).
To choose an alpha channel display option, do one of the following:
m Choose View > Channels, then choose an option from the submenu.
m Choose an alpha channel display option from the View pop-up menu in the Viewer.
Alpha channel display
options
Background display
options