Abstract: Visual artists and designers frequently use carefully crafted motion textures -- patterns of ambient motion throughout a scene -- to imbue the atmosphere with affect. The design of such ambient visual cues is an elusive topic that has been studied by painters, theatre directors, scenic designers, lighting designers, filmmakers, producers, and artists for years. Recent research shows that such motion textures have the capacity to be both perceptually efficient and powerfully evocative, but adding them to scenes requires careful manipulation "by hand": no tools currently exist to facilitate this integration. In this paper we describe the design and development of the aMotion toolkit: a palette of composable motion "brushes" for image and video based on our affective motion research. We discuss insights from an on-going qualitative study with professional visual effects designers into how such capabilities can enhance their current practice.