Colours are objective, according to two philosophers, even though blue you see doesn’t match what I see

By Elay Shech and Michael Watkins for The Conversation

Auburn: Is your green my green? Probably not. What appears as pure green to me will likely look a bit yellowish or blueish to you. This is because visual systems vary from person to person. Moreover, an object’s colour may appear differently against different backgrounds or under different lighting.

These facts might naturally lead you to think that colours are subjective. That, unlike features such as length and temperature, colours are not objective features. Either nothing has a true colour, or colours are relative to observers and their viewing conditions.

But perceptual variation has misled you. We are philosophers who study colours, objectivity and science, and we argue in our book “The Metaphysics of Colours” that colours are as objective as length and temperature.

Perceptual variation

There is a surprising amount of variation in how people perceive the world. If you offer a group of people a spectrum of colour chips ranging from chartreuse to purple and asked them to pick the unique green chip – the chip with no yellow or blue in it – their choices would vary considerably. Indeed, there wouldn’t be a single chip that most observers would agree is unique green.

Generally, an object’s background can result in dramatic changes in how you perceive its colours. If you place a gray object against a lighter background, it will appear darker than if you place it against a darker background. This variation in perception is perhaps most striking when viewing an object under different lighting, where a red apple could look green or blue.

Of course, that you experience something differently does not prove that what is experienced is not objective. Water that feels cold to one person may not feel cold to another. And although we do not know who is feeling the water “correctly,” or whether that question even makes sense, we can know the temperature of the water and presume that this temperature is independent of your experience.

Similarly, that you can change the appearance of something’s colour is not the same as changing its colour. You can make an apple look green or blue, but that is not evidence that the apple is not red.

For comparison, the Moon appears larger when it’s on the horizon than when it appears near its zenith. But the size of the Moon has not changed, only its appearance. Hence, that the appearance of an object’s colour or size varies is, by itself, no reason to think that its colour and size are not objective features of the object. In other words, the properties of an object are independent of how they appear to you.

That said, given that there is so much variation in how objects appear, how do you determine what colour something actually is? Is there a way to determine the colour of something despite the many different experiences you might have of it? Matching colours Perhaps determining the colour of something is to determine whether it is red or blue. But we suggest a different approach. Notice that squares that appear to be the same shade of pink against different backgrounds look different against the same background.

It’s easy to assume that to prove colours are objective would require knowing which observers, lighting conditions and backgrounds are the best, or “normal.” But determining the right observers and viewing conditions is not required for determining the very specific colour of an object, regardless of its name. And it is not required to determine whether two objects have the same colour.

To determine whether two objects have the same colour, an observer would need to view the objects side by side against the same background and under various lighting conditions. If you painted part of a room and find that you don’t have enough paint, for instance, finding a match might be very tricky. A colour match requires that no observer under any lighting condition will see a difference between the new paint and the old.

That two people can determine whether two objects have the same colour even if they don’t agree on exactly what that colour is – just as a pool of water can have a particular temperature without feeling the same to me and you – seems like compelling evidence to us that colours are objective features of our world.

Colours, science and indispensability Everyday interactions with colours – such as matching paint samples, determining whether your shirt and pants clash, and even your ability to interpret works of art – are hard to explain if colours are not objective features of objects. But if you turn to science and look at the many ways that researchers think about colours, it becomes harder still.

For example, in the field of colour science, scientific laws are used to explain how objects and light affect perception and the colours of other objects. Such laws, for instance, predict what happens when you mix coloured pigments, when you view contrasting colours simultaneously or successively, and when you look at coloured objects in various lighting conditions.

The philosophers Hilary Putnam and Willard van Orman Quine made famous what is known as the indispensability argument. The basic idea is that if something is indispensable to science, then it must be real and objective – otherwise, science wouldn’t work as well as it does.

For example, you may wonder whether unobservable entities such as electrons and electromagnetic fields really exist. But, so the argument goes, the best scientific explanations assume the existence of such entities and so they must exist. Similarly, because mathematics is indispensable to contemporary science, some philosophers argue that this means mathematical objects are objective and exist independently of a person’s mind.

Likewise, we suggest that colour plays an indispensable role in evolutionary biology. For example, researchers have argued that aposematism – the use of colours to signal a warning for predators – also benefits an animal’s ability to gather resources. Here, an animal’s colouration works directly to expand its food-gathering niche insofar as it informs potential predators that the animal is poisonous or venomous.

In fact, animals can exploit the fact that the same colour pattern can be perceived differently by different perceivers. For instance, some damselfish have ultraviolet face patterns that help them be recognized by other members of their species and communicate with potential mates while remaining largely hidden to predators unable to perceive ultraviolet colours.

In sum, our ability to determine whether objects are coloured the same or differently and the indispensable roles they play in science suggest that colours are as real and objective as length and temperature.

Elay Shech is Professor of Philosophy at Auburn University and Michael Watkins is a Professor of Philosophy at Auburn University