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To get the context of this question clear, I would like you to walk through some parts of my house.

We'll start with one of my rooms as it appears normally - area Y

As evident, this part of my house has a creamish tinge to it, also the balcony door is open which further gives this room a yellow tint. Nothing special. I'll call it "area Y" (for yellow)*. Let's move on.

area G

Here we arrive in another part of my house which has greenish/blue shades acting as a sunlight blocker. This gives this entire place a greenish/blue tint as shown. (Ref. "area G")

So, now let's visit the area Y again. I am always surprised with what my eyes now see. This. {1}

enter image description here

You see, the same room, same lightning, yet the room now looks much more reddish than before! That's what intrigues me, why does it happen? Why my eyes suddenly become sensitive to red color?

I am not a biology student but I do know that our eyes have cones which specialize in color perception, and that there are different types of cone cells to perceive different types of colors (If I remember my high school biology correctly).

So, I somewhat get a feeling of what's happening inside my eyes (or the brain perhaps?). I suspect that as I go to area G, my eyes 'adapt' to the dominance of bluish/green light, either by decreasing pigment of blue cones or by increasing pigment of red cones, which makes my eyes more sensitive to the other end of visible light spectrum (red-yellow), causing an 'outburst' of red coloration in area 'Y'. Since pigments need time to degrade, by the time the red color pigment of my cones decreases, its activity is less than normal. It may be increased as the blue pigment's activity is less than normal and I see a reddish tinge for few moments.

This was a pure hypothesis from my part, but it seems correct to me. But why do my eyes even adapt to blue color? Why can't my eyes be unbiased towards colors?

{1} Obviously I photoshopped the red tint in the image how else could I have replicated my vision? Though it's not the most accurate description of what I see it's still a very close approximation.

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  • $\begingroup$ Your brain does something roughly similar to auto white balance. Use the camera to take WB from the green room, and then shoot the white room - is that what you meant? $\endgroup$
    – Agent_L
    Commented Mar 19, 2018 at 12:39
  • $\begingroup$ is the WB setting available on a smart phone camera? I don't see it in mine. $\endgroup$
    – sarthak-ag
    Commented Mar 19, 2018 at 13:10
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    $\begingroup$ @Sarthak123 Depends on the camera. Mine lets you set white balance in what it calls "Pro" mode. $\endgroup$
    – David Richerby
    Commented Mar 19, 2018 at 13:49

1 Answer 1

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Short answer
The phenomenon you describe can be explained by the negative afterimage effect, which indeed is elicited by adaptive processes in the retinae.

Background
In the retina there are three types of color photoreceptors, called cones. They are sensitive to red, green and blue, respectively. Colors are processed in the retina through a process explained by the Hering model. This model assumes that there are two sets of opponent colors, namely red - green and blue - yellow (Fig. 1).

This model assumes that in the red-green opponent channel the red cones inhibit the output of green cones and vice versa. In the blue-yellow channel the blue cones inhibit the green/red (= yellow) cone output and vice versa.

Now look at the visual illusion shown in Fig. 2. This illusion nicely illustrates the effect. After looking at the image for half a minute, your cones adapt to the color input. Particularly relevant to your question is that the green cones adapt to the green and become less responsive to green (this happens when you are in your "greenish blue shade acting as a sunlight blocker. This gives this entire place a greenish [blue] tint as shown. (Ref. 'area G')." Now this in turn lowers the green inhibition of the red-half of the red-green opponent channel. In turn, when you enter your "part of [the] house [with] a creamish tinge to it, [] 'area Y' []" the green channel will not inhibit the red-half and everything will have a reddish hue to it, akin to looking at the white half of the illusion after 30 seconds below.

Reference
- Sci Am, October 2013

Hering
Fig. 1. Hering model of color vision. Left panel: brightness coding. Right panel: opponent colors code for color, namely the red-green and blue-yellow channels. source: Bio.SE

After image
Fig. 2. Visual afterimage illusion. Look at the fixation dot in the middle of the tripartite circle on the left for 30 seconds. Don't look away. Now look instantly to the white part on the right. If you don't see much, or only vaguely, try again. Blinking may help to shortly enhance the illusion. source: Sci Am

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    $\begingroup$ The reverse-color image ones were fun as a kid. $\endgroup$
    – JAB
    Commented Mar 18, 2018 at 22:30
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    $\begingroup$ There's more to it than just afterimages. The eye (or the brain) does adapt, though I don't know the mechanism. Perhaps the most obvious case is demonstrated by taking photos at sunset when cross-country skiing. Your eye/brain knows that the snow is white, and sees it as white, or nearly so. The camera records a very reddish color, though. $\endgroup$
    – jamesqf
    Commented Mar 19, 2018 at 3:14
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    $\begingroup$ @Sarthak123 you describe the sunshades as blue. To me, they look green. Assuming they are green, the negative after image is red. $\endgroup$
    – AliceD ♦
    Commented Mar 19, 2018 at 7:19
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    $\begingroup$ I think it's misleading to describe the three sets of cones as "... sensitive to red, green and blue, respectively ...". Each set of cones responds to a wide range of frequencies, to different extents. In fact, the "long wavelength" cones respond more strongly to green than they do to red. So it's badly wrong to refer to "red cones", "green cones" and "blue cones". Other than that, this is a good and thorough answer. $\endgroup$
    – Dawood ibn Kareem
    Commented Mar 19, 2018 at 7:38
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    $\begingroup$ @DawoodibnKareem yes the cone absorption curves are broad. The thing is that the Hering model lies at the basis of sharpening the cone responses, because of the opponencies sharpening their partner's response. So it's not misleading at all. Further, absorption spectra of cones have been the subject of a multitude of questions already. I'm getting tired of posting those good ol absorption curves :-) and in this answer their not essential either. Lastly, the terms red, green and blue cones are used widely in the visual sciences. $\endgroup$
    – AliceD ♦
    Commented Mar 19, 2018 at 7:47

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