Is Indigo Actually a Color of Itself?

Indigo is often a subject of debate and confusion for many. In this article, we will delve into the history, definition, and scientific aspects of indigo, clarifying its place in the spectrum and common misconceptions.

The History of Newton and the Rainbow

Isaac Newton, in his seminal work, described the spectrum of light as containing 7 bands of color. These were:

Red Orange Yellow Green Blue Indigo Violet

However, modern understanding has evolved. Newton’s use of the term "indigo" was likely referring to a shade we now call "blue," and his "blue" might correspond to what we now recognize as "cyan."

Modern Interpretation of the Rainbow

If Newton were alive today and observed the rainbow, he might describe the bands as:

Red Orange Yellow Green Cyan Indigo Blue

This shift in terminology can cause confusion. Various authors and diagrams propose different shades for indigo, but the following diagram from my forthcoming new book (created by one of my PhD students) offers clarity:

Indigo: A slightly reddish blue Violet: Redder than indigo Purple: Even redder, not in the spectrum

It is important to note that indigo, according to Newton’s definition, could be considered blue today.

Color Combinations and Definitions

Indigo is a secondary color created by mixing equal parts of primary colors: red and blue. Primary colors include red, blue, and yellow. Secondary colors result from mixing these primary colors in different ratios. Tertiary colors, like rose and orange, are created by mixing primary and secondary colors.

Visual Perception and Color Mixing

While indigo has a clear definition based on color mixing, the perception of other color combinations can be more complex. Red and blue mixed together form a "purple," even though there is no single wavelength that corresponds to "purple." Similarly, "teal" is a mixture of blue and green, further illustrating the intricacies of color terms in our language.

The term "green," however, stands out. Despite the spectrum of pure green wavelengths, our visual cortex interprets a mixture of yellow and blue as green. This discrepancy highlights the fascinating and often non-linear nature of color perception.

Conclusion

Indigo, as a color, has a rich history and evolving definition. Understanding its place in the spectrum and its relationship to other colors can help clear up misconceptions and enhance our appreciation of the complexities of color theory.

By exploring these definitions and perceptions, we gain a deeper insight into the science and art of color and its role in our lives.

Keywords: indigo, color theory, spectral colors