For all those who, through curiosity, have discovered or may discover their interest in the fascinating field of chemistry

Nothing shows us the beauty of our world as vividly as its colors. For our distant biological ancestors, there were predominantly smells. However, at some point in our long evolution into modern humans, we dared to swap the dull magic realm of scents for the bright precision of our eyes. And yet colors are also a magical realm that holds many a secret. Unlike shape, density, or surface texture, color is not an inherent property of an object but only our perception of how the object reflects or absorbs visible light. Moreover, our eyes show us only a tiny fraction of the immense spectrum of electromagnetic radiation that fills our universe. The wavelengths, and thus the frequencies, of this spectrum span 16 orders of magnitude—from the 10 to 20 km long radio waves of some military transmitters to the gamma rays of imploding galaxies, which are only a thousandth of a nanometer short. Life on our planet mainly registers wavelengths between 300 and 1000 nm. This range includes the ultraviolet, with wavelengths below 400 nm, which unlike many insects, we cannot see; the range from blue to green to red, that is, from 400 to about 750 nm, which means light to us; and finally, infrared rays, with wavelengths above 800 nm, which some animals perceive as light but we perceive only as heat.

Ultraviolet was probably the first color that life on our planet saw. This spectral part of sunlight meant danger, as it destroyed many biological building blocks. Cells developed a sensor for ultraviolet and blue light that controlled the direction of rotation of their flagella to avoid these dangerous rays. Since these flagella act as propulsion propellers, the cells could now not only see the harmful short-wave light but also avoid it. A descendant of this blue light sensor is still found today in many primitive protozoa.

This ingenious blue light sensor probably also served the cells as a construction ma