  Motion graphic (MG) videos are effective and compelling for presenting
complex concepts through animated visuals; and colors are important to convey
desired emotions, maintain visual continuity, and signal narrative transitions.
However, current video color authoring workflows are fragmented, lacking
contextual previews, hindering rapid theme adjustments, and not aligning with
progressive authoring flows of designers. To bridge this gap, we introduce
Piet, the first tool tailored for MG video color authoring. Piet features an
interactive palette to visually represent color distributions, support
controllable focus levels, and enable quick theme probing via grouped color
shifts. We interviewed 6 domain experts to identify the frustrations in current
tools and inform the design of Piet. An in-lab user study with 13 expert
designers showed that Piet effectively simplified the MG video color authoring
and reduced the friction in creative color theme exploration.
