1. History

In 1932 the first chairman of the Inter-Society Color Council (ISCC), E. N. Gathercoal, proposed that the Council develop "a means of designating colors in the United States Pharmacopoeia, in the National Formulary, and in general literature such designation to be sufficiently standardized as to be acceptable and usable by science, sufficiently broad to be appreciated and used by science, art and industry, and sufficiently commonplace to be understood, at least in a general way, by the whole public." This problem originally was referred by the ISCC to its Committee on Measurement and Specification which, under the chairmanship of I. H. Godlove, presented several reports surveying available methods of color designation. The 1933 annual report of this committee [22] included the outline of a recommended system of color designations. These recommendations were approved by the Council and followed by the authors in developing this system of color designations, in setting the color boundaries, and in working out methods of applying the system to drugs and chemicals in various forms. The Inter-Society Color Council in 1939 formally approved by letter ballot [20], and recommended to the National Formulary Revision Committee and to the United States Pharmacopoeial Convention, the method described in NBS Research Paper RP1239 [27] Since 1939, a number of suggestions for revision of this system of color names have been received, especially from Margaret Hayden Rorke, Managing Director of the Textile Color Card Association (TCCA), which have aided the authors in

1 Figures in brackets indicate the literature references on pages 13 and 14.

making the present revision. An ISCC committee consisting of Beck, Clark, Foss, Godlove, Granville, Judd (Chairman), Kelly, Nickerson, Reimann, Rorke, and Stearns was formed in 1947 to study these suggestions and make recommendations as to name and boundary changes. The changes which are embodied in this revision have been approved by the letter ballot [21] for use wherever applicable by all of the 19 Member Bodies and the Individual Member Group of the ISCC.

2. Scope

The color designations have been extended to apply under the recommended conditions of lighting and viewing not only to opaque surfaces such as prepared powder samples or solids but also to clear or cloudy liquids or solids, microscopic structures and fluorescent samples. The gamut of color names has been extended to cover the colors of clear and cloudy lighttransmitting samples by substituting colorless for white, faint pink for pinkish white, faint yellow for yellowish white, faint green for greenish white, faint blue for bluish white, and faint purple for purplish white [20].

It must be remembered that the Munsell renotations and the ISCC-NBS color names used in this system are determined under the conditions of average daylight (CIE source C), 45° illumination, and normal viewing (see section 6.1.2). In determining Munsell approximate renotations by comparison with the Munsell scales, the sample must be about the same size as the Munsell chips and must be viewed on a white or light gray background. These conditions will be referred to in this paper as "recommended conditions of lighting and viewing" or simply

conditions the ISCC-NBS color names agree well with common usage. Use of other light sources (such as incandescent-lamp light or light from the mercury arc) will yield object colors not correctly described by these names.

In contradistinction to the color-name charts published in RP1239 [27] which were based on Munsell book notations, the charts in this revision are based on Munsell renotations. However, the color names resulting, from the use of these charts with Munsell book notations will be sufficiently appropriate for all usual purposes. If the precise designation is desired, the conversion from notation to renotation may be read from Final Report of the OSA Subcommittee on the Spacing of the Munsell Colors as in section 6.1.3 [42] and the color name obtained in the usual way.

3. Applications

Aside from the use of the ISCC-NBS system of color names in the National Formulary and the United States Pharmacopoeia for which they were originally developed [29], they are finding increasing use in fields where extreme accuracy or sales appeal are not needed but where a simple, definite, easily understood color designation is desired. Publications in the fields of ceramics [45], chemistry [33, 50], dermatology [2], dyestuffs [46], lights [28], mica [17], interior and exterior painting [3], paper [26], plastics [5, 6], rocks [40], soils [43, 47, 51, 55], stone [31], textiles [54], and general description [1, 18, 25], will give some idea of the type of applications for which these names are used.

4. Logic of Designations

To fulfill the requirements of the problem stated by E. N. Gathercoal, especially comprehension by the public, it was decided to use the simplest color designations possible but to define the individual color ranges so designated as accurately as possible. The hue names were chosen for simplicity and descriptiveness: red, orange, yellow, green, blue, violet, purple, pink, brown, and olive. Adjectival forms of these hue names are used in the compound designations such as reddish orange, greenish yellow, purplish red. These hue names are preceded by appropriate modifiers (light, dark, pale, deep and so on) also chosen for simplicity and easy understanding. Therefore, the designations for all but very grayish colors consist of a hue name preceded by appropriate modifiers. The designations for very grayish colors consist of a noun (white, gray, or black) with modifiers appropriate to the lightness and hue of the colors, such as dark reddish gray or yellowish white.

4.1. The Color Solid

In order to understand the color-name blocks used in this system, it will be best to visualize the psychological color solid as shown in figure 1. Imagine a grapefruit set on the table so its pithy core is vertical. Imagine also that the top of this core is white

FIGURE 1. Dimensions of the color solid.

and that the bottom is black with the intermediate grays in between. Next imagine the spectrum hues the nonspectrum violet to red region filled in with stretched around the equator of this grapefruit with the proper purple colors. Then fill this solid with all colors that a surface may have, thinking of each surface color as a point, with the light colors near the top of the solid and dark ones near the bottom. Grayish colors will naturally be near the core with the more saturated colors near the peel. In such a solid, lightness will be measured up from the base plane of the table, or black, to the top of the core,

or white. Saturation will be measured outward from hue will be measured by angle around the core. Furthe core with the strongest colors on the peel, and ther imagine that all colors falling on one of the will be of the same hue, all samples falling in one of vertical planes intersecting in the black-white axis the horizontal planes through the solid will be of the same lightness, and all colors falling on concentric cylinders about the black-white axis will be of the

same saturation.

A. H. Munsell envisioned a system of color standards [10, 13, 30, 35, 36, 48, 49] embracing all colors organized on this plan. Under ordinary observing conditions, the "Munsell value" of a sample correlates closely with the lightness of the color perceived to belong to the sample, while the "Munsell chroma" correlates well with the saturation of the color perceived to belong to the sample [19, page 47].

Now imagine this Munsell color solid with the primary hues evenly spaced around the equator giving the closed series red, yellow, green, blue, purple and red, with their intermediates. The hue half-way between each two of these primary hues is given a

two-word name making five additional Munsell hues: yellow-red, green-yellow, blue-green, purple-blue, and red-purple. These ten are called the major hues and to each one is assigned, consecutively on the equator of the solid, ten divisions numbered from one to ten (see pages 31 to 34), giving a 100-point hue scale with each major Munsell hue placed at the middle of its 10-point spread, or at division 5, as 5R, 5YR, 5Y, 5GY, and so forth. In this way, there are 10 steps between each major hue indicating graduated steps of hue around the hue circuit. Ten secondary Munsell hues are included in the system, namely: 10R, 10YR, 10Y and so on, one between each adjacent pair of major hues. These secondary hues fall on the number ten positions of each set of ten hue divisions. Therefore, each major Munsell hue is understood to be at division five whereas each secondary hue is understood to be at division ten of the preceding major hue. The Munsell Color Company has now produced similar charts that come at 2.5 and 7.5 or midway between each pair of adjacent primary and secondary charts [13]. Each of these charts consists of colored rectangles all of the same Munsell hue arranged in rows and columns, light colors near the top of the chart, dark near the bottom, grayish colors to the left and strong to the right.

The Munsell scale of value exhibits 10 visually equal steps ranging between black (represented by the notation N 0/) and white (N 10/), the intermediate chips being dark to light grays. The Munsell value of a color is the same as that of the gray sample in the same row of the constant-hue charts, and is recorded in front of a shilling mark, thus 6 value is written 6/.

Munsell chroma is the degree of difference of a color from a gray of the same value and is indicated by steps numbered outward from the neutral axis. Therefore all samples in any vertical column of the constant-hue charts have the same Munsell chroma. Munsell chroma notations follow the shilling mark, thus 2 chroma is written /2. Colors of one Munsell hue are therefore represented in the solid by points falling in a single one of the vertical planes intersecting at the black-white axis. Colors of one value are represented by points in any one horizontal plane; and colors of one chroma are represented by points in any one of the series of right circular cylinders concentric about the black-white axis.

The complete notation is written in the order: Hue Value/Chroma or H V/C with a space between the H and the V/C; for example, 5R 6/3 means a red of value 6 and chroma 3, and 6YR 6.8/6.6 means a yellow-red (orange) of value 6.8 and chroma 6.6 whose hue departs from the 5YR chart toward the 7.5YR chart by two-fifths of the hue difference between those charts.

4.2. Basic Plan of Forming the Designations The hue name of the color designation is intended to indicate a range of hue represented by an angle around the neutral axis in the color solid, and other words in the designation are to indicate ranges of value and chroma for this hue range. The system of modifiers is indicated in figure 2 together with the

Saturation (Munsell Chroma) FIGURE 2. Scheme of the hue modifiers, the "-ish" grays and the neutrals with their modifiers. Abbreviations are given in parentheses.

approved abbreviations. Deviations from the moderate range in value are indicated by the terms light and dark; deviations in chroma by the terms grayish, strong and vivid; and deviations in both by the terms light grayish or pale, dark grayish, blackish, brilliant and deep The whole color designation, hue name and modifiers, therefore defines a block of the color solid bounded by vertical planes of constant hue, horizontal planes of constant value, and cylindrical surfaces of constant chroma. The color solid is divided into 262 such blocks including the grays and "-ish" grays with 5 cylindrical blocks for black, grays, and white making 267 color-name blocks in all.

4.3. Divisions of the Hue Circle

The 1933 recommendations by I. H. Godlove included a 20-point division of the hue circle for colors of moderate saturation, a 10-point division for weak colors and a 5-point division for very weak colors. These recommendations were followed closely at first with the thought that each color designation should refer to about the same fraction of the Munsell hue circuit. However, it was soon evident that deviations from this plan were necessary to make the designations accord with usage at that time in the National Formulary and the United States Pharmacopoeia, and more recently with usage in the textile industries and by the general public. Most of these improvements were achieved by introducing the terms pink, orange, brown, and olive

and the elimination of the double terms blue-green, purple-blue, and red-purple.

Unlike the terms green and blue, which are hue names applying to all lightnesses and saturations, the term yellow is commonly used to designate not only a certain hue range but also a high lightness range within this hue range. Dark colors of the same hue as yellow are commonly called olive or olive brown. Common usage limits the term orange even more strictly; it is taken to refer not simply to a range of yellow-red hues but also to a mediumlightness range and a high saturation range. Colors of the same hue but of lower lightness and saturation than the orange range are called browns.

date may be separated by many hours, but on the other hand two scarcely separable midnight events. may have to be assigned different dates. Just as identifying the time of an event by giving the date has proved to be useful, so it is with a system of color designations such as this.

5. Definition of the Color Ranges

The definitions of the boundaries of the 267 color subcommittee of the Inter-Society Color Council in name blocks or ranges have been carried out by the terms of the Munsell renotations [41, 42] which approximate more closely the ideal psychological color system than does the 1929 edition of the Munsell Book of Color.

observation of all of the color standards obtainable for which Munsell renotations were available. These included the chips of the Munsell Book of Color [42], some of the chips of the Maerz and Paul Dictionary of Color [44], the ninth edition of the Standard Color Card of America published by the Textile Color Card Association of the United States Inc. [54], and the Color Harmony Manual [11].

The subcommittee checked the color boundaries

4.4. Some Unavoidable Disadvantages

A frequent objection to this system of color designations is that each designation refers to a group of distinguishable colors rather than to a single color. Since there are about ten million surface colors distinguishable in daylight by the trained human eye and less than 300 color designations in this system, it is obvious that the average color range denoted by a single designation must contain nearly 40,000 distinguishable colors. If it is important to make distinctions among some of these thousands of colors bearing by this system identical designations, resort must be had to one of the many numerical systems of color specification available. Preeminent among these is the colorimetric coordinate system recommended in 1931 by the International Commission on Illumination (CIE) [16, 24, 53].

A corollary to this objection is that there are many pairs of easily distinguishable colors which receive by this system the same designation, while there are also many pairs that can scarcely be distinguished which receive different designations. This property is, of course, an unavoidable result of dividing the color solid into an arbitrary number of blocks, one for each of the 267 designations. Analogous disadvantages result from identifying the time of events according to date; two events occurring on the same

The boundaries for the color-name blocks found

by the subcommittee to accord with common usage are given in 31 color-name charts (pages 16 to 31). They are more complicated than those of the original ISCC-NBS system and differ importantly from one level of Munsell value to another. The changes of the boundaries with Munsell value are shown in seven constant-value charts (pages 31 to 34) on which the Munsell hue is indicated in the 100-point scale. The chart for value 4.75 refers to colors of medium lightness and shows 17 hue ranges, the other constant-value charts refer to lighter or darker colors than the first chart as indicated by their respective value notations. The value levels of these charts were picked so that every different hue or chroma boundary in the 31 colorname charts would show on one of them. The hues are indicated on these constant-value charts by the abbreviations shown in table 1.