The book "Colorimetry in Instrumental and Visual Test Analysis" offers a comprehensive analysis of chemical colorimetry and its application in the study of functional materials as well as in environmental analytics. The authors, Sergei Vladimirovich Himchenko and Lyudmila Petrovna Jexperiandova, systematically present the results of their research and demonstrate how colorimetry can be utilized as an independent physicochemical method in materials science and in both visual and instrumental analysis. A central theme of the book is the development of precise color test scales based on a probabilistic approach to maximize the accuracy of the analysis. The authors show that the minimal step for specific color nuances corresponds to the Golden Ratio, which minimizes the error rate in the analysis. Additionally, simple methods for non-laboratory analysis of natural water are presented, which can be conducted both visually and with portable devices. This specialized book is aimed at scientists, educators, and students in the chemical and physicochemical disciplines.