[saspinski]

There is a nice video in youtube about this subject. It a lot more about light polarization, but at the end the demonstration is impressive.

[opportunity]

"But", I've never heard of or experienced a reddish hue, which understandably puts me off guard. In fact I've never heard of it until this post. So it's a real phenomena?

With no red cones, you would not be fully sensitive to the dominant color at sunrise & sunset.

Just to understand the impact, How bright do red traffic lights appear to you?
- Are they the same intensity and color as green (just up the top), or  is the red light almost black?
- Do the newer LED-based traffic lights appear different than the older incandescent traffic lights?

I understand that for dichromats, there is a pure color around light blue which is indistinguishable from white.
For trichromats (most of us), all pure (rainbow) colors are clearly different from white.

Apologies for not replying sooner, didn't see your reply.

I've had a "lot" of trouble, and so I usually look at the red part cautiously, making sure it is "illuminated". That's easy to see, the illumination, provided the sun is not shining behind me.

The first indication was in my first year driving when I turned right on a red arrow, my mother sitting next to me asking whether I saw the red, I didn't. The sun was behind us, so the imprint of the "red" light was not apparent as it usually is with the normal brightness traffic lights give.

Then in my first year Uni I did extra work working as a courier......I didn't see a stop sign (red) in front of a tree (green) and went through it on one of my deliveries, looked to my right and saw the smoke of a car locking up. Terrifying. I still didn't think it would be a big issue until all the nuances of red in med-school became apparent.

To answer your question, the "brightness" of the light is what I depend on.  When the sun is shining behind me, it's very difficult to know what's happening with red traffic lights.

LED, I think it's about the brightness also, haven't noticed any big problems knowing to look for "brightness".

As for a colour around blue indistinguishable from white, no, never noticed that. White is white.. Blue is blue. There is in fact a lot of definition between those two (for instance, I've designed a website with blue and white (<<COMMERCIAL LINK REMOVED>>), because to me the colours are most striking.....and yes I didn't consider once again it's because of my protanopia).

[evan_au]

why does a rainbow have seven colours right? That's the next question, right?

The podcast below had some interesting comments on colors in different languages.

Some linguists (Berlin & Kay) did a study of many languages, looking at common color words that would be used by children, for example.
- They excluded technical or specialist words that would be used in specific contexts

They found that every language had 2 words that were equivalent to light or white, and dark or black.
- But they found that other languages had 3, 4, 5, 6, 7 or more color words,
- And they concluded that languages generally added color words in a particular order:
- black+white, then red, green or yellow, then green + yellow, blue, etc (if I remember correctly)

The speaker suggested that Old English in the 1200s had words for white, black, red, yellow, and green.
- Purple was present, from the color of European royalty (but from the Romans)
- Violet was later added from the color and name of the flower
- Orange was added later, from the color and name of the fruit

Since white and black are not colors of the rainbow, one assumes that an Old English rainbow would have had perhaps 4 major bands of color.

I'm not sure I believe some of what he says, but listen to the last 10 minutes of: http://historyofenglishpodcast.com/2017/12/31/episode-106-an-illuminating-discovery/

If you listen to the whole episode, you will hear a bizarre explanation for why Romance languages like French use words like "blanc" for white, while English, a Germanic language uses "black" for black - and yet they are derived from the same Indo-European root word!

[opportunity]

why does a rainbow have seven colours right? That's the next question, right?

The podcast below had some interesting comments on colors in different languages.

Some linguists (Berlin & Kay) did a study of many languages, looking at common color words that would be used by children, for example.
- They excluded technical or specialist words that would be used in specific contexts

They found that every language had 2 words that were equivalent to light or white, and dark or black.
- But they found that other languages had 3, 4, 5, 6, 7 or more color words,
- And they concluded that languages generally added color words in a particular order:
- black+white, then red, green or yellow, then green + yellow, blue, etc (if I remember correctly)

The speaker suggested that Old English in the 1200s had words for white, black, red, yellow, and green.
- Purple was present, from the color of European royalty (but from the Romans)
- Violet was later added from the color and name of the flower
- Orange was added later, from the color and name of the fruit

Since white and black are not colors of the rainbow, one assumes that an Old English rainbow would have had perhaps 4 major bands of color.

I'm not sure I believe some of what he says, but listen to the last 10 minutes of: http://historyofenglishpodcast.com/2017/12/31/episode-106-an-illuminating-discovery/

If you listen to the whole episode, you will hear a bizarre explanation for why Romance languages like French use words like "blanc" for white, while English, a Germanic language uses "black" for black - and yet they are derived from the same Indo-European root word!

That's fascinating. Blanc as black, yet its white; I know French and never made the connection. Could be a way of suggesting in words black is defined by white, or vice-versa? Very very interesting. Christian mythology rooted the idea of the light overcoming the darkness, blanc-de-blanc (technically, "champagne") it would seem.....

[Bill S]

Currently, I have my own example of variable colour vision.  Yesterday, I had a cataract Op.  The new lens "blue-shifts" my colour vision.  If I ask myself which eye sees the "true" colour, the answer must be both, or neither.  Things don't have an intrinsic (correct) colour as far as our vision is concerned.

BTW; if there is anyone out there with a cataract who has doubts about having the Op. I would say, go for it ASAP.

[Colin2B]

The new lens "blue-shifts" my colour vision.  If I ask myself which eye sees the "true" colour, the answer must be both, or neither.

The eye that has had the cataract removed.
As I understand it the lens goes yellowish with age, so as yellow is complementary to cyan I would expect you to think your vision has gone blueish with a clear lens.

[Bill S]

As I understand it the lens goes yellowish with age, so as yellow is complementary to cyan I would expect you to think your vision has gone blueish with a clear lens.

That makes good sense to me.