Speaking of color illusions and smell, here is a fascinating experiment:

Participants sniffed bottles of colored (red, green, and yellow) and colorless water while blind-folded and while not. Each nostril was tested separately. Here are the results:

“Although no thermal stimulus was present, subjects reported thermal sensations, but only under free viewing conditions. The nature of these sensations depended on the color of the solution, with green inducing cooling and red warming sensations.” Graph from Michael and Rohlion.*

When participants could see the color of the water, they had the illusion of temperature sensations just as if the trigeminal nerve in the nose had been activated. In a follow-up study, when participants were just looking at a bottle of colored water while sniffing a bottle of plain water that they couldn’t see, these researchers saw the same effect, suggesting that the mere presence of a colored water can cause the brain to perceive an illusory state.**

Remember how the oenology students perceived the white-wine-dyed-red  as being spicy and peppery? Spicy and peppery are sensations brought about normally by activation of the TRPV1 “hot” receptor of the trigeminal nerve in the nose. Which raises the question: did these students in fact experience this color-temperature illusion, and—given the lack of the word “warm” in the vocabulary they had to use—chose “spicy” and “peppery” instead?

It appears that the association of color with temperature is so strong in the brain, that we subconsciously ascribe temperature to colored substances. How this association comes about, in other words whether it is innate or learned, is unknown. In favor of innate is the failure to make the same associations between the learned odor of lavender and lavender the color. 

My overall conclusion: rather than laugh at wine experts for being fooled and conclude that wine experts are not truly experts, we should realize that we all make the association between color and other sensory modalities to a greater or lesser degree. The effect is something we seem not to be able to avoid, whether we are expert or naïve.

* George A. Michael, Pauline Rolhion. Cool colors: Color-induced nasal thermal sensations. Neuroscience Letters. Volume 436, Issue 2, 9 May 2008, Pages 141–144.

** George A. Michael, Hélène Galich, Solveig Relland, Sabine Prud’hon. Hot colors: The nature and specificity of color-induced nasal thermal sensations. Behavioural Brain Research. Volume 207, Issue 2, 5 March 2010, Pages 418–428