Colour Classes
The class limits shown below (Fig. 3) have been chosen after examination of the Munsell colour charts and the scheme used for grouping in the Factual Key (Northcote 1979). A major aim was to achieve class limits as simple as possible and to standardise on these throughout the system. The proposed scheme has the virtue of simplicity although some may argue that 2.5YR 4/2 for example is not very grey, nor is 5YR 8/3 very red. These discrepancies can of course be removed, but at the cost of simplicity. Some of the more obvious 'misfits' are probably rare in soils. Colours should be matched to the chip closest in colour, or the nearest whole number in chroma where chips are not provided, for example chromas 5 and 7.
Figure 3. Colour class limits.
| Black | The dominant colour (moist) for all hues has a value of 3 or less and a chroma of 2 or less. |
| Red | The dominant colour (moist) has a hue of 5YR or redder and a chroma of 3 or more. |
| Brown | The dominant colour (moist) has a hue yellower than 5YR and a value of 5 or less and a chroma of 3 or more. |
| Yellow | The dominant colour (moist) has a hue yellower than 5YR and a value of 6 or more and a chroma of 4 or more. |
| Grey | The dominant colour (moist) for all hues has a value of 4 or more and chroma 2 or less; for hues yellower than 5YR values of 6 or more and chromas of 3 are allowed. |