Back in 2006 an American neurobiologist named Mark Changizi published research suggesting that human colour vision evolved to give us the ability to interpret the health and emotional states of others based on blanching and reddening of the skin, as in "blushing" for example. Here is his 2006 paper on the subject:

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1618887/

And his 2010 book "The Vision Revolution":

https://www.amazon.com.au/Vision-Revolution-Research-Overturns-Everything/dp/1933771666?ref=d6k_applink_bb_dls&dplnkId=d8b64177-a217-4ca9-afd5-fe4e939c6bf9

Of particular interest, he has founded a company called Vino Optics which has developed a range of eyeglasses which are designed to enhance specific aspects of colour perception, with one item in the range called the "FreeX" sunglasses being speficically designed to enhance the perception of colour variations on a person's skin. This obviously has an application to the NPA model, given the significance of blanching and reddening of the skin in the context of anger (or embarrasment/blushing) associated with the Aggressive and Sanguine traits respectively, and even more importantly given the distinction between Sanguine types and non-Sanguine types in terms of baseline facial complexion, noticeably tending toward ruddiness and pallor respectively in these two categories. Given that this is often somewhat discernable to the naked eye, I'm curious to find out if it's the case that when wearing these glasses the presence or absence of the N trait generally becomes much more starkly and immediately apparent; could non-sanguine types become - in many cases - instantly identifiable with the aid of this device?

"FreeX Sunwear is the world's only sunwear augmenting color vision as nature intended. Our patented Oxy-Amp lens technology augments your ability to see colors in the world, and especially the expressive states of people: their blushes, blanches, flushes and other subtle color changes. You're not usually consciously aware of your ability to read others via this evolved instinct, but you do it daily. It's part of your natural intuition.

Our technology takes that intuition to
the next level"

"Color vision is for seeing the blushes, blanches, flushes and other emotions on the bare skin of others, a seminal discovery by VINO OPTICS scientists. Those same scientists then patented technology that further augments that capability"

Link to purchase FreeX Sunglasses:

https://www.vino.vi/collections/color-enhancing-lenses/products/freex-glasses-round-mirrored

More information on FreeX Sunglasses:

https://www.oxfordstudent.com/2012/10/02/through-the-looking-glass-the-feelings-behind-the-facade/

https://changizi.wordpress.com/tag/sunglasses/

https://www.prosocial.world/posts/how-mark-changizi-conquered-colorblindness-with-glasses

https://www.scientificamerican.com/article/new-eyewear-could-help-people-with-red-green-color-blindness/

https://www.smithsonianmag.com/smart-news/glasses-let-doctors-poker-players-see-your-blood-126300530/

https://www.thenationalnews.com/business/glasses-to-help-you-see-the-colours-of-the-rainbow-1.647692#amp_tf=From%20%251%24s&aoh=17010958515738&csi=1&referrer=https%3A%2F%2Fwww.google.com&share=https%3A%2F%2Fwww.thenationalnews.com%2Fbusiness%2Fglasses-to-help-you-see-the-colours-of-the-rainbow-1.647692

https://www.technologyreview.com/2012/06/19/255718/i-see-right-through-you-glasses-to-read-peoples-skin/#amp_tf=From%20%251%24s&aoh=17010958515738&csi=1&referrer=https%3A%2F%2Fwww.google.com&share=https%3A%2F%2Fwww.technologyreview.com%2F2012%2F06%2F19%2F255718%2Fi-see-right-through-you-glasses-to-read-peoples-skin%2F

https://www.forbes.com/sites/daviddisalvo/2012/07/01/new-sunglasses-let-you-see-anothers-emotions-really/#amp_tf=From%20%251%24s&aoh=17010958515738&csi=1&referrer=https%3A%2F%2Fwww.google.com&share=https%3A%2F%2Fwww.forbes.com%2Fsites%2Fdaviddisalvo%2F2012%2F07%2F01%2Fnew-sunglasses-let-you-see-anothers-emotions-really%2F

More information on the colour vision research by Mark Changizi:

https://www.dailynews.com/general-news/20060305/blush-may-key-vision-linked-to-rise-of-color-sensors/

https://www.newscientist.com/article/dn8703-colour-vision-evolved-to-spot-our-blushes/

https://www.caltech.edu/about/news/old-world-primates-evolved-color-vision-better-see-each-other-blush-study-reveals-1103

https://www.sciencebase.com/science-blog/mark-changizi-vision-revolution.html

https://www.2020mag.com/article/a-different-color-perspective

https://healthland.time.com/2012/07/06/why-humans-have-color-vision-and-other-qs-as-with-neuroscientist-mark-changizi/

https://www.nbcnews.com/id/wbna11644771

https://blogs.scientificamerican.com/guest-blog/the-mores-of-makeup/