Many philosophical debates are haunted by Locke’s thought experiment of spectrum inversion: “if the idea that a violet produced in one man’s mind by his eyes were the same that a marigold produced in another man’s, and vice versa” .
Austen Clark attempted to prove rigorously that spectrum inversion would be detectable by observing the subjects’ response to colours [2, 3]. He argued as follows: Suppose that two people perceive mutually inverted spectra and agree in their judgements of visual stimuli and the relations between them. Therefore, the colour solid (i.e. the visible colours as co-ordinates in some space) must exhibit symmetry. Since this solid (represented in three-dimensional Euclidean space e.g. as the Munsell colour system ) is in fact asymmetric, the premise must be false.
Can you spot the fallacy? It stems from assuming that everyone’s colour solid is identical. Clark mistook a textbook model for the real thing — a fallacy known as reification. Both the Munsell colour system and other proposed colour solids abstract away from differences in visual perception that occur among observers and even across experiments with the same observer [5–9]. One can easily conceive of a personal colour solid that remains the same (within measurement error) when mirrored or rotated. If there cannot be people who function like us with a mirrored or rotated colour solid, it is not its asymmetry that forbids their existence.
 Locke, John. “An Essay Concerning Human Understanding”, book II, ch. XXXII, par. 15. http://humanum.arts.cuhk.edu.hk/Philosophy/Locke/echu/lok0042.htm#15
 Clark, Austen. Spectrum Inversion and the Color Solid. Southern Journal of Philosophy, vol. 23, no. 4, Winter 1986, pp. 431–443. http://selfpace.uconn.edu/paper/CSOLID.HTM
 Clark, Austen. “A Theory of Sentience”. Oxford University Press: 2000. pp. 17–18. http://citeseerx.ist.psu.edu/viewdoc/download?doi=10.1.1.85.5641&rep=rep1&type=pdf#17
 Webster, Michael A.; Eriko Miyahara; Gokhan Malkoc; Vincent E. Raker. Variations in normal color vision. I. Cone-opponent axes. Journal of the Optical Society of America, vol. 17, no. 9, September 2000, pp. 1535–1544. http://www.ncbi.nlm.nih.gov/pubmed/10975363
 Webster, Michael A.; Eriko Miyahara; Gokhan Malkoc; Vincent E. Raker. Variations in normal color vision. II. Unique hues. Journal of the Optical Society of America, vol. 17, no. 9, September 2000, pp. 1545–1555. http://localhopf.cns.nyu.edu/events/vjclub/archive/webster2000.pdf
 Webster, Michael A.; Shernaaz M. Webster; Shrikant Bharadwaj; Richa Verma; Jaikishan Jaikumar; Gitanjali Madan; E. Vaithilingham. Variations in normal color vision. III. Unique hues in Indian and United States observers. Journal of the Optical Society of America, vol. 19, no. 10, October 2002, pp. 1951–1962. http://wolfweb.unr.edu/homepage/mwebster/assets/pdfs/WebsterJOSA2002.pdf
 Malkoc, Gokhan; Paul Kay; Michael A. Webster. Variations in normal color vision. IV. Binary hues and hue scaling. Journal of the Optical Society of America, vol. 22, no. 10, October 2005, pp. 2154–2168. http://www1.icsi.berkeley.edu/~kay/mkw.josa.2005.pdf
 Juricevic, Igor; Michael A. Webster. Variations in normal color vision. V. Simulations of adaptation to natural color environments. Visual Neuroscience, vol. 26, no. 1, January 2009, pp. 133–145. http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2684467/