I present a slightly old (but still relevant) article on Apple Motion. Here are Ten things you should know about Apple Motion (thanks to DV.com).
For example:
DIRTY ALPHA
Not happy with the alpha channel you get when you cut a Motion project into a Final Cut Pro timeline? Well, your alpha may be off. Final Cut Pro sometimes misinterprets the alpha channel data, expecting you to have a straight alpha channel, when in fact you may have a premultiplied alpha.
1. Select the Imported Motion project file in your Browser.
2. Choose Modify > Alpha Type Black.