In Memoriam: Professor Rolf G. Kuehni (1938–2026)

Abstract

The international color science community has lost one of its most influential scholars, historians, educators, and dedicated stewards with the passing of Professor Rolf Georg Kuehni on April 12, 2026, at the age of 88. A former Editor of Color Research and Application, an internationally respected authority in color science and technology, and a passionate advocate for color education, Professor Kuehni's legacy is deeply interwoven with the development of modern color science and with the many individuals and institutions he influenced throughout his remarkable life.

Born in Langnau im Emmental, Switzerland, Rolf Kuehni came from an old Swiss family and spent his early years in the town of Schönenwerd, where his father worked as a shoe designer for the Bally Shoe Company. From an early age, he was immersed in an environment where craftsmanship, materials, and aesthetics were closely linked. He later moved to Krefeld, Germany, where he studied textile chemistry at Fachhochschule Niederrhein, receiving his degree in 1961.

Following graduation, Prof. Kuehni began working at CIBA in Basel, Switzerland, under the supervision of Dr. Paul Ulrich, a research chemist with broad interests in color science and color literature. Ulrich introduced the young Kuehni to early psychological and scientific writings on color, helping to spark what would become a lifelong intellectual journey. Although Prof. Kuehni initially focused on practical problems related to dye strength determination through transmittance and reflectance measurements, he soon became deeply aware of the limitations of existing instrumentation and methods during a period of rapid technological development.

In 1963, he moved to the United States, eventually becoming a dual citizen. Two years later he joined Verona Dyestuffs, owned by Bayer Corporation, where he served as Manager of Development and Color Physics. This role marked the beginning of his pioneering involvement in computer colorant formulation and color quality control. Recognizing the transformative potential of emerging technologies, Prof. Kuehni persuaded management to acquire an IBM 1130 computer, which enabled the development of advanced approaches to color formulation and measurement at a time when industrial color computation was still in its infancy.

Over the course of his industrial career, Professor Kuehni advanced to senior leadership positions, including Vice President Marketing/Textile Products for Bayer Corporation in the United States and later Vice President of DyStar Corporation. Yet even while carrying major executive responsibilities, he maintained a deep and sustained commitment to color science research and scholarship. He consistently sought to bridge industrial practice with theoretical understanding, helping connect color technology with the broader scientific study of human color perception.

Professor Kuehni's scientific contributions spanned an extraordinary range of topics, including color tolerancing, indices of metamerism, theoretical foundations of metamerism, color difference evaluation, color spaces, and the modeling of hue perception. He was especially noted for challenging assumptions and asking penetrating questions about the relationship between color metrics and human visual experience. His work often highlighted the complexities and limitations of existing color spaces and color-difference formulas, encouraging the field to reconsider accepted paradigms and pursue a deeper understanding of perceptual variability.

Throughout his career, Professor Kuehni was a strong advocate for closer ties between industrial scientists engaged in practical color technology and academic scientists investigating visual perception and the foundations of color science. He believed that progress in color science required continuous dialogue between application and theory, between engineering and perception, and between historical understanding and future innovation.

His intellectual curiosity extended far beyond technical color measurement. Professor Kuehni possessed a rare breadth of scholarship that integrated science, history, philosophy, art, and culture. He became widely recognized not only as a color scientist and technologist, but also as one of the foremost historians of color science.

As Editor of Color Research and Application from 1987 to 1989, Professor Kuehni played a pivotal role in shaping the journal during a period of important growth and intellectual expansion. He helped broaden the journal's scope and influence by encouraging interdisciplinary scholarship and by making historically important European scientific writings accessible to English-speaking audiences. Among his many editorial and scholarly contributions were translations of seminal works by scientists such as Johann Heinrich Lambert, Arthur König, Wilhelm Ostwald, Rudolf Luther, Erwin Schrödinger, and Philipp Otto Runge. These translations, many published through Color Research and Application and the Inter-Society Color Council (ISCC), opened foundational historical texts to new generations of scholars.

Professor Kuehni remained deeply connected to the journal throughout his life as an author, reviewer, editor, mentor, and advisor. Colleagues consistently admired his rigor, clarity, historical knowledge, and unwavering commitment to advancing the discipline.

A prolific scholar, Professor Kuehni authored or co-authored approximately 80 scientific and technical papers, encyclopedia entries, and nine influential books. Among the most important of these was Computer Colorant Formulation (1975), the first major text to explain the scientific and engineering principles underlying computer-based color formulation systems used throughout the coloration industries. Significantly, he introduced the term “colorant formulation” in place of “color matching,” terminology that remains widely used today.

His widely respected text Color: An Introduction to Practice and Principles demonstrated his remarkable ability to synthesize the technical, perceptual, historical, and artistic dimensions of color into a coherent and compelling narrative. The book addressed not only classical color science topics such as colorimetry, color calculation, colorants, and color reproduction but also broader subjects including color harmony, color theory in art, and the history of color in science and culture.

Another landmark publication, Color Ordered: A Survey of Color Systems from Antiquity to the Present, co-authored with Andreas Schwarz, is widely regarded as one of the definitive treatments of color order systems. The work traced the historical evolution of color ordering from simple linear scales to sophisticated multidimensional systems, illustrating Prof. Kuehni's unparalleled command of both the scientific and historical development of color organization.

His passion for the history of color science also culminated in Pioneers of Color Science, co-authored with Renzo Shamey and published in 2020. The volume documented the lives and achievements of approximately one hundred historic figures whose contributions shaped the field of color science.

Professor Kuehni also contributed extensively to the Encyclopedia of Color Science and Technology, serving as section editor for Vision Phenomena and Vision Physiology and authoring numerous entries. He further served on editorial boards, acted as a reviewer for scientific journals, and provided thoughtful guidance and mentorship to younger researchers and professionals.

His contributions extended well beyond publications and editorial work. Professor Kuehni played an active role in major professional organizations including the Inter-Society Color Council (ISCC), the American Association of Textile Chemists and Colorists (AATCC), and the International Commission on Illumination (CIE). Within the CIE, he served as a member or advisor on several important technical committees, including those addressing uniform color spaces, improved color matching functions, and unique hue data.

Colleagues on these committees often remarked upon his exceptional historical memory, analytical precision, and ability to provide fresh perspectives on longstanding scientific problems. His questions were famously incisive yet constructive, consistently helping researchers refine their assumptions and sharpen their thinking.

Professor Kuehni's many honors reflected both the breadth and depth of his influence. In 1986 he received the Armin J. Bruning Award from the Federation of Societies for Coatings Technology in recognition of his contributions to colorimetry in the paint and coatings industries. In 2005 he received the prestigious AATCC Olney Medal for outstanding scientific contributions to textile coloration and color science.

The Inter-Society Color Council recognized his extraordinary service and scholarship with several of its highest honors, including the Godlove Award in 2003, the Nickerson Service Award in 2015, and the Munsell Centennial Award for Science in 2018.

When receiving the Godlove Award, Professor Kuehni reflected characteristically on both the mysteries and the future of color science. He emphasized that much about human color perception remained unknown and expressed his conviction that important scientific challenges still awaited younger generations of researchers. He believed deeply that color science remained a vibrant and evolving field, full of unanswered questions about visual variability, color appearance, and perceptual organization.

One of the defining features of Professor Kuehni's career was his dedication to education and mentorship. Following his retirement from industry, he served as Adjunct Professor of Color Science at North Carolina State University from 2002 to 2018. During this period, he taught lectures on color science and visual perception, mentored students and faculty colleagues, supervised student projects, and continued active research collaborations.

At North Carolina State University, Professor Kuehni worked closely with Professors Renzo Shamey, David Hinks, and others in advancing color science education and research. Students valued not only his immense knowledge but also his intellectual honesty, curiosity, and willingness to engage deeply with difficult questions. He challenged students to think critically, to question assumptions, and to appreciate the historical and philosophical context of scientific inquiry.

Those who knew Professor Kuehni personally will remember not only his scholarship and scientific rigor, but also his generosity, humility, wit, and kindness. He possessed a rare combination of intellectual intensity and genuine warmth. Conversations with him often moved effortlessly between technical color science, philosophy, art, history, and everyday human experience. Professor Roy Berns reflected that “he was a big influence during my formative years becoming a color scientist,” while Professor Ronnier Luo described him as “a great leader in the field” who continually urged researchers “to strive for robust observer data,” praising his book on color space for providing “a complete story” of its development and demonstrating “an in-depth understanding of colour science.” Roy Osborne simply noted that “his contributions were outstanding,” and Professor Rossi wrote that “the international color research community has lost a scholar of great value and an authoritative point of reference.” Professor MacDonald highlighted Kuehni's landmark text Color: An Introduction to Practice and Principles as “very clear and informative, and a credit to its author,” adding that as editor of Color Research and Application he did much to promote color science as a truly interdisciplinary field. Dr. Wyble remembered him as “an old master,” while Professor Da Pos described him as “a great thinker, open to understand and discuss different viewpoints.” Eric Kirchner called him “one of the smartest color scientists of the past decades,” praising both the breadth of his scholarship and works such as Color Ordered, which he described as “an incredibly beautiful but also a thorough overview of color ordering systems throughout history.” Professor Martin Bide, former President of AATCC, perhaps summarized him best: “Rolf was a true polymath. He presented and shared his knowledge in a kind and gentle way.”

He was deeply committed to preserving the historical foundations of the field while encouraging innovation and new thinking. Whether discussing color spaces, translating historical manuscripts, mentoring students, or debating theoretical issues at conferences, Professor Kuehni consistently approached his work with passion, integrity, and intellectual courage.

His influence extended across generations and continents. Researchers, students, practitioners, educators, and colleagues throughout the world benefited from his scholarship, mentorship, and friendship. His writings continue to serve as foundational references, and his questions continue to shape ongoing discussions in color science and visual perception.

Professor Rolf G. Kuehni leaves behind an enduring scientific and intellectual legacy that will continue to inform and inspire future generations of color scientists, educators, historians, and practitioners.

We extend our deepest condolences to his family, friends, former colleagues, students, and the worldwide color science community.

The author has nothing to report.

The author declares no conflicts of interest.