1) Try changing the alpha channel interpretation by selecting the underlying media in the Media tab of the Project Pane, then going to the Media tab of the Inspector
2) John Knoll’s Unmult plugin should work fine in Motion, but been awhile since I tested it
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Mark Spencer
Freelance Producer/Editor/Motion Graphics Artist
Apple-certified Master Trainer
Author, Motion 4 from Peachpit Press
https://www.applemotion.net