The delay? I don't think we're in a hurry. And clearly no one else on the list 
has an interest in our discussion.

Spectral colors and their perception are my business. I've made literally 
billions of square meters of diffraction gratings, mostly decorative patterns. 
Yellow and magenta have been particularly interesting to me for a few reasons. 
I am of the controversial opinion that yellow doesn't exist except in human 

Years ago, before lasers became unbelievably inexpensive, I was interested in 
creating a light source to view transmission holograms without a laser or 
filtered mercury arc. I had a lot of slide projectors left over from my 
"psychedelic light show" so I thought I could use one to make such a light 
source. I put a slit into the projector where the slide would normally go and a 
high efficiency Bragg diffraction grating in front of it. This projected a nice 
broad spectrum. I then used another slit to isolate whatever color I wanted and 
a cylinder lens to spread it out. This worked quite well, but not very bright. 
I settled on what would normally be called the yellow part of the spectrum.

But people viewing the holograms this way would say that the color was white, 
or perhaps gray. I thought the same thing. You have to see this to appreciate 
it. So maybe Roy G Biv should change his name. Another example of the 
phenomenon is a pressure tuned krypton laser. At just the right gas pressure it 
makes four more or less equally spaced colors if sent through a prism: red, 
yellow, green, and two tightly spaced blues. The yellow looks yellow when the 
other colors are present, but by itself it appears to be colorless. A lot of 
people smarter than I have argued about these things for a very long time.

If you really want to see some strangeness as regards color perception, look up 
Land color theory. I played around with this when I was a child, and my family 
thought I was nuts.

I just think it's a gift to us that we can perceive color the way we do.

------- Original Message -------
On Thursday, August 24th, 2023 at 9:10 AM, H L V <> wrote:

> Sorry about the delay.
> I am not sure. If you think about it, overlapping colours don't go along with 
> the topology of stress lines.
> However, cellophane tape is a different situation. It could be that the 
> perception of the colour magenta is situational like
> the perception of yellow.
> Did you know that a third class of mammalian photoreceptors was discovered in 
> the 1990's?Intrinsically photosensitive retinal ganglion cell were only shown 
> to be definitively present in humans in 2007 in people who were born without 
> rods and cones.
> From wikipedia " ipRGCs were only definitively detected in humans during 
> landmark experiments in 2007 on rodless, coneless 
> humans.[15]([16](
>  As had been found in other mammals, the identity of the non-rod non-cone 
> photoreceptor in humans was found to be a ganglion cell in the inner retina. 
> The researchers had tracked down patients with rare diseases wiping out 
> classic rod and cone photoreceptor function but preserving ganglion cell 
> function.[15]([16](
>  Despite having no rods or cones the patients continued to exhibit circadian 
> photoentrainment, circadian behavioural patterns, melanopsin suppression, and 
> pupil reactions, with peak spectral sensitivities to environmental and 
> experimental light matching that for the melanopsin photopigment. Their 
> brains could also associate vision with light of this frequency."
> Harry

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