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 color systems       color solid | munsell | rhs | ucl | hcc | ridgway || related pages

This page describes the color solid, and gives information about a number of formal color description systems.

 color solid
The color solid helps to conceptualize color terminology. Thinking of it as a globe:
  • the axis is black at the bottom, lightening to white at the top
  • the least saturated colors are along the axis, with the saturation increasing toward the surface of the globe
  • hues change horizontally around the axis
  • all colors on a vertical plane intersecting the axis are the same hue
  • all colors on a horizontal plane through the axis are the same value or lightness
  • all colors on a concentric cylinder about the axis are the same chroma or saturation

 munsell
The Munsell Color System, published as the Munsell Book of Color, contains over 1500 color standards which are visually equally-spaced scales of hue, value and chroma. The equal spacing facilitates visual interpolation to about 100,000 different colors by an experienced observer.

With reference to the above color solid, Munsell names an intermediate hue between each of those shown, giving Red, Yellow Red, Yellow, Green Yellow, Green, Blue Green, Blue, Purple Blue, Purple, Red Purple, all spaced evenly around the equator of the globe. The Munsell notation describes a color in terms of its hue, value and chroma, e.g., 3.7R 4.0/11.4 (a strong red), where:
- 3.7R is the hue, described by a number from 1 to 10 and the hue abbreviation, where the number is the left-to-right location in the hue, such that 1R is close to 10RP, and 10R is close to 1YR;
- 4.0, the number before the /, is the value or lightness from 1 (black) to 10 (white); and
- 11.4, the last number, is the chroma or saturation from 0 at the axis to around 18 at the surface.

Munsell is active in industrial color applications, as described at their Solutions page. Munsell also publishes different books of standard colors, and sells a variety of color management hardware and software.

 royal horticultural society
The Royal Horticultural Society (RHS) has been publishing the RHS Colour Chart since 1966. Early editions had 202 numbered hues, printed as 4 lightnesses each, named A, B, C and D, for a total of 808 colors identified, e.g., as RHS 53B, which is strong red. They are arranged as four fans with pages about 2.5'' by 7.5'', with four color patches for one hue on one page. Later editions have a hole in each color patch, to view the object being matched surrounded by the color patch.

The editions are identified by the boxes used to enclose the fans:
  • 1966 - green cardboard box, removable top
  • 1986 - silver gray plastic box, fliptop
  • 1995 - dark green plastic box, fliptop
  • 2001 - red and black plastic box, fliptop (884 colors)
Since there are slight color differences between the editions, the recommended approach to identifying a color is to include the year of the edition used, such as RHS66 53A, which is deep red. The 76 new colors introduced in the 2001 edition, and some of the previous red-purple and blue colors now printed as solid colors, are to be prefaced with the letter N, such as RHS01 N47A, which is orange red.

The 2001 edition is available through the RHS for £135 (~$210) plus S&H.

Approximations of the colors in the RHS Colour Chart, along with the corresponding Universal Color Language numbers and names, can be seen at RHS colors. Although these colors were developed from accurate data supplied by Munsell, they only roughly approximate the true colors of the RHS Colour Chart for several reasons:
- they are shown as background colors, which are limited by some web browsers to a 216-color palette, rather than the thousands or millions of colors possible with color images;
- some of the colors are "out of gamut" and cannot be shown accurately on computer monitors;
- the data were computed for a gamma of 1.4, better suited for Macintosh than for Windows monitors; and
- the RHS Colour Chart is printed (subtractive color using ink), while the onscreen colors are displayed (additive color using light).

A rigorous attempt to show the RHS Colour Chart onscreen is described at RHS Colors on a monitor.

 universal color language
The Universal Color Language (UCL) was defined by the Inter-Society Color Council - National Bureau of Standards in 1946. Each of the 267 UCL color names gives an idea of the named color without reference to color chips, by combining a very few standard and well known color terms. A valid UCL color name can be a a hue only, e.g. pink, or a hue modifier plus a hue, e.g. yellowish pink; or a value/chroma plus a hue modifier plus a hue, e.g. light yellowish pink . Each such UCL color name is quite useful for garden planning purposes, although it describes too broad a range of colors to describe a plant for identification purposes.

Click here for a list of some common color names and their UCL equivalents, and more information about UCL names, or click here for a visual overview of the UCL, and an index to an exhaustive list of color names (including the Ridgway names used to describe Glenn Dale azaleas) and their corresponding UCL numbers, names, and onscreen color chips.

The UCL is documented in COLOR Universal Language and Dictionary of Names, NBS Special Publication 440, 184 pages (December 1976). Most of the text is the dictionary of names, which relates UCL names to the names used in 14 other color systems, including Ridgway. Although it is out of print, the National Technical Information Service will provide a PDF file or print a color copy of it for $64 plus S&H. Call the NTIS order desk at 1-800-553-6847 and ask for it by their number PB-265 225.

 horticultural colour chart
The British Colour Council, in collaboration with the Royal Horticultural Society, published the Horticultural Colour Chart in 1938. It includes 200 named hues, printed as 3 lightnesses each for a total of 600 colors. They are identified by name and number, e.g., Cardinal Red, 822/1, which is strong red.

The Horticultural Color Chart is out of print.

 ridgway
Robert Ridgway published a book of 1,115 named colors in 1912, entitled "The Standardization of Colors and Color Names", intended for use by in the natural sciences. The Glenn Dale azaleas were originally described using these names. For example, 'Ambrosia' is Begonia Rose (deep yellowish pink), 'Andros' is Mallow Pink (strong purplish pink), 'Bowman' is Eosine Pink (deep pink), 'Oriflamme' is Tyrian Rose (vivid purplish red), and 'Seneca' is Mallow Purple (strong purple).

The Ridgway book is out of print.

 related pages
color help (parent page)

Updated July 29, 2005

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