It sounds like you have some motion tracking and rotoscoping to do, unless you can use the colors of the flowers alone to isolate them from the rest of the scene. If the flowers are a unique color, you can get away with just the Leave Color effect.
———————————————————————————————————
Todd Kopriva, Adobe Systems Incorporated
putting the ‘T’ back in ‘RTFM’ : After Effects Help on the Web
———————————————————————————————————
If a page of After Effects Help answers your question, please consider rating it. If you have a tip, technique, or link to share—or if there is something that you’d like to see added or improved—please leave a comment.