Color plays a crucial role in app design, second only to functionality, as it helps set the mood and guide user interaction. This tutorial demonstrates how to implement dark mode and theme a Next.js app using the styled-components library and the useDarkMode Hook. Dark mode, which displays light text on a dark background, offers benefits such as energy savings and reduced eye strain compared to the more common light mode. The styled-components library provides enhanced developer experience by allowing component-scoped CSS, automatic vendor prefixing, and unique class names, while the useDarkMode Hook simplifies theme switching without manual state management. By integrating these tools, developers can dynamically switch between themes and create visually appealing user interfaces. Additionally, the tutorial addresses the "flicker" issue that occurs with server-side rendering by using a mounted state to ensure the correct theme is displayed upon page load, enhancing the app's user experience.