With the popularization of mobile internet and the rapid development of short video platforms, short video public service announcements (PSAs) have become an important medium for social welfare communication. Compared to traditional broadcast media, short video PSAs, with their immediacy and interactivity in narrative and communication methods, as well as their color rhythm and visual tension, can quickly attract audience attention and evoke emotional resonance, significantly improving communication effectiveness. Therefore, this paper analyzes the media characteristics and color design requirements of short video PSAs, and explores the design strategies of color rhythm from the perspectives of theme positioning, rhythm changes, and audience psychology. It also examines methods for constructing visual tension in short video PSAs from the perspectives of composition design, visual elements, and dynamic effects, aiming to enhance the communication effectiveness and social impact of public service announcements.