Calculate "Color Development Equivalent" by the method of Buntley & Westin (1965) "A Comparative Study of Developmental Color in a Chestnut-Chernozem-Brunizem Soil Climosequence" DOI: 10.2136/sssaj1965.03615995002900050029x. Originally developed for Mollisols, the Buntley-Westin index has been used as a tool to separate soils based on depth to particular colors.
buntley.westin.index(hue, chroma)A numeric vector reflecting horizon color development.
Buntley, G.J. and Westin, F.C. (1965), A Comparative Study of Developmental Color in a Chestnut-Chernozem-Brunizem Soil Climosequence. Soil Science Society of America Journal, 29: 579-582. doi:10.2136/sssaj1965.03615995002900050029x