The ongoing COVID-19 pandemic has shown that the world needs technology that can quickly and accurately identify invisible dangers, including harmful substances or airborne environmental pollutants. Colorimetric sensors—devices that intuitively reveal information about their environment through color changes—are an attractive option in this regard. But, for more people to benefit from these sensors, they must be easy to produce at a large scale. This is a major limitation with currently available colorimetric sensors, which require complex structures with intricate fabrication procedures. Other problems with existing devices include slow response times and unsaturated colors.