Blue (B), yellow (Y), red (R), and green (G) color-changing dye was used in a general chemistry course for first-year undergraduate students with nonscience majors to highlight the redox reactions written as the gain and loss of hydrogen. The first experiment is a vibrant color variation using a synthetic dye of indigo carmine. The second experiment is dyeing using the natural colorant of dry Japanese indigo leaves that have been used to make indigo-colored fabrics with a centuries-old method. The third experiment is a color change achieved using fresh Japanese indigo leaves. The three indigo-based experiments give a clear appearance, an experience regarding a traditional process, and a facile method, respectively. The visual impact and historical process that starts from surrounding natural materials makes a significant impression on students. The course contents were introduced in a lesson within 30 min to empower the teaching of redox reactions by showing oxidized and reduced forms of the indigo dye chromophore. The outcome was that an increasing number of students could explain the definition of oxidation in organic reactions in terms of the gain or loss of hydrogen.