The ability of the ISCC-NBS Method to describe colors with different levels of accuracy was applied many times during the development of this method. For instance, the Munsell Notation of a paint chip or a finely ground drug sample [1, 45] can be determined by a trained observer under good lighting and viewing conditions (sec. 6.1.2, CND) to one half of a hue step, to one tenth of a value step and to three tenths of a chroma step. This accuracy is more than that necessary to determine the appropriate ISCC-NBS color name descriptive of the color of the drug sample, for instance. Now, suppose that the ISCC-NBS color name of this drug sample were "light yellowish brown". The same drug sample could be described less accurately as simply "yellowish brown". It could be described with still less accuracy by the simple generic hue name "brown". Thus we can see that three levels of accuracy of color designation are possible with color names alone (see table 1).

Now let us consider another type of example. Mrs. Smith has just told us she bought a "green" sofa. This color name tells us only that this color falls somewhere in the green part of the color solid; that is, it is not a red, yellow, blue or purple. Let us call this most basic type of color designation level 1. If, however, she had said it was a yellowish green, then we would have known also that it was not a plain green or a bluish green. Let us call this finer type of color designation level 2. If she had gone. further and described the color of her new sofa as a light yellowish green, then we would have had a very good idea of its color. Let us call this still more specific type of color designation level 3. (Naturally, we are assuming in this discussion that all the people involved have normal color vision.)

Thus it can be seen that through the use of the ISCC-NBS Method of Designating Colors, three correlated levels of accuracy of color description can be delineated using color names alone. So, the ISCC-NBS Method not only supplies the basis of what we will call The Universal Color Language, but it also supplies the first three levels of increasing fineness of color designation of this language. A color designation can be a color name, numbers, letters or a combination of two or of all three of these.

However, even three levels of fineness of color designation are not sufficient to meet the demands of science, art and industry. The usefulness of color names is limited to levels 1, 2 and 3. Where still greater accuracies of color designation are requiredthat is, where the color solid is divided into larger and larger numbers of smaller and smaller blocksletters and/or numbers will be required to designate these colors.

An obvious choice to be used in level 4, the next level of accuracy higher than level 3, is the Munsell Book of Color [3, 22, 30, 32] containing just over 1500 color standards. In response to the demands for still greater accuracy, the visually interpolated Munsell notation was the logical selection for level

5. This is the level used in most applications of the Munsell Book of Color in science, education, art. and industry. The practical limit of visual interpolation among these color standards has been reached in level 5. As a result, the next higher level of accuracy of color designation, level 6, must be based on instrumental measurements. A spectrophotometer is the preferred instrument but certain. colorimeters can be used at this level of accuracy provided the conditions of measurement are carefully controlled. (See sec. 10, level 6). The results from these instrumental measurements can be expressed in the CIE coordinate system (x, y, Y or X, Y, Z) [2, 17, 19, 38] or in a more finely interpolated Munsell notation determined mathematically from the CIE coordinates.

While levels 4, 5 and 6 are not expressly described in the ISCC-NBS Method of Designating Colors, they are logical extensions of this Method. Remember that the boundaries of the color-name blocks in the color-name charts [sec. 13, CND] are defined in Munsell terms. Remember also that the appropriate ISCC-NBS Color Name description of a color is determined through a visually or instrumentally determined Munsell notation.

Through the determination of the Munsell notations of the individual color samples in two well known collections of color standards (the 9th Standard Color Card of America [7, 41] and the Horticultural Colour Chart [6, 33]), fig. 7, these collections can be used in place of the Munsell Book of Color in visually determining the ISCCNBS Color Names in level 3. By the same use of equivalent Munsell notations, it is possible to use four other color-order systems in place of Munsell in level 4. These are Maerz and Paul, 1st Edition [26, 34], Plochere [28, 40], Ridgway [12, 43] and the Color Harmony Manual, 3rd Edition [10, 11, 16, 34, 44], figure 8.

3. The Universal Color Language

It is difficult to trace the origin of the name The Universal Color Language [14, 15, 21, 23] except to state that it coincided with the development and extension of the ISCC-NBS Method of Designating Colors.

Although reference has already been made to the concept of six levels of color designation, historically the notion of levels evolved during the solution of ISCC Problem 23, the Historical Expression of Color Usage [14, 21]. The Color Marketing Group (CMG) was formed in June 1962 [8, 21]. They adapted this method to the statistical analysis of color trends-the changing patterns of color usage in the various industries in which product color is an important marketing factor. That level is used which is appropriate to the degree of accuracy of color designation needed in the particular application, the accuracy increasing with the level number. The higher levels represent a finer division of the whole color solid into a greater number of smaller blocks of color.

It was approximately 1963 that the name The Universal Color Language (UCL) was coined in discussions with the Executive Secretary of the Color Marketing Group. The name indicates the very wide range of applications available depending on the demands of the user, including variable levels of accuracy and the use of varying types of color designations (color names or letter and/or number designations). It must be borne in mind that the UCL describes only the color of an object. It does not describe any of the other appearance attributes, such as gloss or texture. When these other appearance attributes are likewise standardized and reduced to a language, then the UCL will become part of the larger, more inclusive Universal Appearance Language (UAL).

The UCL is being increasingly used in science, education, art and industry. It has the open-ended flexibility to add level 7 when a still more accurate designation of color is needed. By the same token, it can also add intermediate levels such as 2B or 2C between levels 2 (29 blocks) and 3 (267 blocks). Such an intermediate level can be made to contain perhaps 80 to 150 color designations, if this number is required for a special purpose. As a special dividend, the UCL has the unique ability to translate for the first time the special color names of the wellknown color-order systems and collections of color standards into the ISCC-NBS color names, or from one of these special color languages into one of the others. These special color languages include Ridgway (ornithology, geology, botany, biology), Plochere (interior decorating), Color Harmony Manual, 3rd edition ("mass market", items on the market shelf), Maerz and Paul, 1st edition (historical color names), the Nickerson Color Fan (flower colors) [35, 36], Dade (biology) [9, 12, 43], the 9th Standard Color Card of America (fashion, flag colors), and the Horticultural Colour Chart (flower colors). When a new color-order system, such as the Natural Color System of Sweden, is published and the individual colored samples are assigned Munsell notations, it will likewise be possible to translate these new designations into the ISCC-NBS color names or into one of the special color languages listed above.

It is important to remember that in each level. (a) the whole color solid is divided into a stated number of blocks, (b) the boundaries of each color-name block are accurately specified and (c) all six levels. are related through the UCL. Table 1 summarizes the six levels of accuracy of color designation and their applications. One arrow indicates the direction to go for greater accuracy of color designation. The other arrow indicates the direction taken in the statistical combination or "roll-up" technique used in statistical studies of color trends by the Color Marketing Group.

The UCL has resulted from a massive cooperative effort by organizations and individuals all interested in realizing the utmost benefits from color in every field of application. To use a mechanical simile, it can be likened to a bridge over which color informa

tion flows in both directions between the salesman and the customer, or between the scientist and the manufacturer or management. The UCL is the second Supplement to the Color Names Dictionary.

4. The ISCC-NBS Centroid Colors

The ISCC-NBS Centroid Colors [15, 20] (fig. 9) were developed to illustrate the center (center-ofgravity or centroid) of each of the 267 color-name blocks [sec. 13, CND]. These standard colors are in the form of one-inch square glossy paint-on-paper samples affixed on a variable gray background so that each color is seen on a background of approximately its own lightness. Under each Centroid Color is the abbreviation of the appropriate ISCCNBS color name plus the corresponding Centroid or color-name-block number (fig. 10). These color samples illustrate the central or most typical color of each of the color-name blocks. With a set of Centroid Colors, we can now see directly what the average person is supposed to mean when he uses one of the ISCC-NBS color names. Since the block number, the corresponding ISCC-NBS color designation and the Munsell notation of each of the Centroid Colors are listed in the table attached to each set of these charts, the Centroid Colors form an extremely useful and inexpensive set of special color standards. The ISCC-NBS Centroid Color Charts form the first Supplement to the Color Names Dictionary.

4.1 Other Advantages and Applications of the Centroid Colors

Another advantage associated with the Centroid Colors is the use of the Centroid number as an abbreviation of the ISCC-NBS color designation. This number (ranging from 1 to 267) requires only three columns on a computer punch card, such as an acquisition or inventory card. It is also possible to code the color of an item on a single data-processing card at each of the six levels. In fact this has already been done on a commercial basis by the Color Marketing Group.

Another advantage results from the color-nameblock structure of the ISCC-NBS Method of Designating Colors. Since the hue, value and chroma boundaries of each color-name block enclose the ranges of color best described by that ISCC-NBS color name, these boundaries can be considered color-name tolerances around each ISCC-NBS color name. To put it another way, each such boundary separates the ranges of color best described by the contiguous ISCC-NBS color names.

Each level of the UCL will now be discussed separately and in the detail required to apply it to color problems which can be solved with the accuracy of color designation inherent in that level.

5. Level 1

In level 1, the whole color solid is divided into just 13 large color-name blocks. As a result, each of