For most purposes a general colour direction seems to be most used by gardeners. That said a discourse on detailed colour naming is of interest.

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 colours 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 colour patches for one hue on one page. Later editions have a hole in each colour patch, to view the object being matched surrounded by the color patch. There are currently four editions 1966, 1986, 1995 and 2001.

Since there are slight colour 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 colours introduced in the 2001 edition, and some of the previous red-purple and blue colours now printed as solid colours, are to be prefaced with the letter N, such as RHS01 N47A, which is orange red.

Universal Colour Language

The Universal Colour 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 colour without reference to colour chips, by combining a very few standard and well known colour terms. A valid UCL colour 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 colour name is quite useful for garden planning purposes, although it describes too broad a range of colours to describe a plant for identification purposes.