These are threshold data in u’v’Y’ colourspace. The experiment was carefully controlled for illumination, and used stimuli derived from multispectral measurements of skin textures. Observers made the judgements in an odd-one-out, 4-alternative forced-choice task. A link to the data will be made available shortly.
Reference: Chauhan, T., Xiao, K., & Wuerger, S. (2019). Chromatic and luminance sensitivity for skin and skinlike textures. Journal of Vision, 19(1), 13–13. [doi]