14  Horizon colour

Modified

September 20, 2025

14.1 Colour recording

The colour of soil components is recorded using the Munsell Soil Colour system (Munsell Color Company 2009; Pantone 2017), which conceptualises colour using Hue, Value and Chroma parameters. Table 14.1 shows some example soil colours and their representation in the Munsell system as well as their approximate translations into other colour spaces. A comprehensive primer on colour and its application in soil science can be found in (Bigham and Ciolkosz 1993).

Table 14.1: Examples of Munsell Colour codes and their approximate matches in other systems.
Munsell RGB Hex
10YR5/4 148, 118, 80 #947650
7.5YR3/2 88, 69, 55 #584537
5R3/8 130, 41, 48 #822930
N4/0 97, 97, 97 #616161

For accurately describing colour:

  • The colour charts must be used in clear direct or non-dappled indirect daylight. Avoid describing colours in the early morning, late afternoon, in dappled light or in deep shade. Avoid using damaged or faded colour books.
  • Record the moist colour to standardise the readings across profiles. Use a spray bottle to gently wet up a sample, if necessary, or wait for a saturated sample to dry out slightly. In both cases wait until the sample surface is no longer glistening.
  • Remove sunglasses and turn to keep the main light source behind your shoulder.
  • The sample may not perfectly match any one chip; record the closest match available. Do not interpolate between chips.

Operators need full colour vision to use the Munsell colour system correctly. While diagnosed colour blindness is relatively rare, many people have minor colour-recognition limitations without knowing it. Taking a colour vision test periodically is recommended.

Obtaining soil colour information from digital photographs is possible, but the photographs must meet certain requirements. See Roudier et al. (2016) and Kirillova et al. (2021) for more information. Direct electronic colour sensing devices are available commercially, and research into using smartphones as colour-sensors is ongoing (Mancini et al. 2020; Sinclair et al. 2024).

14.2 Matrix colour

The matrix colour of the soil is the dominant ‘background’ colour. This excludes the colours of redox-induced mottles.

14.2.1 Method: Determining matrix colour

  • Take a 2-3 cm3 sample of fresh soil from the target horizon, avoiding colour transition zones (e.g. horizon boundaries). If large enough peds are available, extract a ped and break it open to expose a fresh face. Otherwise, cut or scoop a fresh sample from the soil mass.
  • Moisten the sample lightly before assessing the colour, by holding the sample up against the chips in the colour book. Hold the sample just in front of a colour chip for comparison. Look for a colour where the sample appears to fade into the chip.
    • Do not record the colour of a texture bolus or a smeared surface, as these can be altered by mixing in mottles or destroying ped surface features.
    • For sands, which may have differently-coloured grains from multiple parent materials, colour matching can be difficult. Try to pick the colour of the dominant mineral component. Holding the sample out at arms’ length may also help determine a dominant colour.

Additional colour information can be stored as free-text notes.

14.2.2 Recording matrix colour

For routine assessment, record the single dominant matrix colour per horizon. For detailed assessment, up to three matrix colours may be recorded if necessary. It is assumed that multiple matrix colours are co-dominant, otherwise the subdominant ones must logically be recorded as colour patterns (Section 14.3).

Dry soil matrix colours are sometimes necessary as well, e.g. for diagnosing a bleached E horizon. If moist and dry matrix colours are both obtained for a horizon, append them with their moisture status as D or M.

Example: 10YR52 M / 10YR71 D.

Naming soil horizons and classifying soils according to the NZSC requires, in many cases, the ability to identify ‘low chroma colours’. These colours have:

  1. a moist chroma of ≤ 2, or
  2. a moist chroma of 3 and a value ≥ 6.

Visually, the red outline in Figure 14.1 contains the low chroma colours. These are in the same location on any given page in the Munsell colour book. Additionally, all of the colours on the Gley and White pages qualify as low chroma.

Figure 14.1: One page from the Munsell Soil Colour Chart book, with the low-chroma colours outlined in red.

14.3 Colour patterns

For most assessments, only pattern type (Section 14.3.1) and abundance ( Section 14.3.2) are required in addition to the pattern colour itself. Further detail is optional, but descriptive measures for pattern shape, size and distinctness are provided below.

14.3.1 Pattern type

Soil colour patterns are most commonly driven by redox processes affecting iron and/or manganese-dominated minerals, but can also be a product of parent material weathering, water movement, or mixing. Record pattern type using the codes in Table 14.2.

Table 14.2: Types of soil colour pattern
Code Name Description
M Mottles Colour patterns induced by redox processes
R Structural Colour patterns induced by preferential flow
W Weathering Colour patterns induced by parent material weathering, most commonly seen in BC horizons and below (e.g. rock ghost patterns)
X Mixing Colour patterns created by biological (e.g. worm tunnels) or mechanical (e.g. landslide) means

14.3.2 Pattern abundance

Estimate the areal percentage of the cut exposure face occupied by the colour pattern, versus the matrix colour. Use the visual guides in Section 21.2.3 to help estimate accurately. Abundance data can be classified according to Table 21.4 where needed.

For example, M 7.5YR58 25% for a bright orange redox mottle observed in moist soil conditions.

14.3.3 Pattern shape

Record pattern shape using the codes in Table 14.3.

Table 14.3: Types of soil colour pattern shape
Code Name Description
B Blotches Rounded shapes, blobs, where colour patterns penetrate the soil mass
S Stripes Linear colour patterns e.g. root linings
C Coatings Patterns caused by ped surface features e.g. cutans

14.3.4 Pattern size

Estimate the average size of each pattern in mm, e.g. 5 ± 2 mm. Pattern size may be classified against Section 21.1.1 if necessary.

14.3.5 Pattern contrast

Rules for determining contrast in the field are defined in Table 14.4. If both matrix and pattern colours are recorded using the Munsell system, contrast can be calculated automatically. Complete rules for automating this process are found in Schoeneberger et al. (2012), section 2-15.

Table 14.4: Types of soil colour pattern contrast
Code Name Description
F Faint Indistinct colour variation evident only on close examination. The secondary colour is typically of the same hue as the primary colour and will generally differ by no more than one unit of chroma or two units of value.
D Distinct

Although not striking, the colour variation is readily seen. The secondary and primary colours usually:

  1. Have the same hue. but differ by more than one and less than four units of chroma, or more than two and less than four units of value, or
  2. Differ by one hue (2.5 Munsell units) and not more than one unit of chroma or two units of value.
P Prominent

The colour variation is conspicuous. The secondary and primary colours normally differ by

  1. At least two full hues (5 Munsell units) if chroma and value are the same, or
  2. At least four units of value or chroma if the hue is the same, or
  3. At least one unit of chroma or two units of value if there is a difference of one full hue (2.5 Munsell units).

14.3.6 Pattern boundary distinctness

Record pattern boundary distinctness using the codes in Table 14.5.

Table 14.5: Types of soil colour pattern distinctness
Code Name Description
S Sharp Knife-edge boundaries between colours.
C Clear Colour transition < 2 mm wide
D Diffuse Colour transition > 2 mm wide

14.3.7 Colour short codes

For rapid recording of pattern colour, the single letter codes in Table 14.6 can be used.

For example, M O 25% for a bright orange redox mottle observed in moist soil conditions.

Colour short codes must not be used for recording the matrix colour(s), as they do not provide enough detail for soil classification.

Table 14.6: Short codes for major soil colours, adapted from (National Committee on Soil and Terrain 2024, p. 137–8). NB: The Munsell colour ranges given are a general guide only, do not interpret them strictly.
Code Name Description
R Red 2.5YR or redder, with value < 7 and chroma > 2
O Orange 5YR or 7.5YR, with value < 7 and chroma > 2
B Brown 7.5YR or 10YR, with value > 4 and chroma > 2
Y Yellow 2.5Y or 5Y, with value > 4 and chroma > 2
G Grey Any non-gley hue, value 4--7, chroma 1
D Dark Any non-gley hue, values ≤ 3 and chromas ≤ 2
P Pale Any non-gley hue, values ≥ 7 and chromas ≤ 2
L Gley Gley charts