“It’s a question of which is to be master, that’s all.”
Even if we didn’t exist, if a naturally occuring quartz crystal were to break up light into it’s component parts, that light would be scattered into different “colors.” Whether or not there was someone around to observe the differences, the differences would exist.
Now, before you beat me to death. I’m a chemist. I don’t know shinola about philosophy.
Isn’t this somewhat akin to whether a falling tree makes a sound in the forest, if there’s no one around to “hear” it.
The “brown” object doesn’t have the same properties as a “green” object, does it?
I would argue that “color” is, in fact, an inherent property of an object. When light shines on an object, it will absorb some, reflect some, and transmit some. The absorbtion, reflection, and transmission will all be governed by functions of various parameters, notably the frequency of the incident light. One can sort the reflection functions into a variety of categories based on various feaures of those functions, and one such possible category is “brown”.
Now, I’ll admit that non-humans might well have a different set of color receptors, and therefore a completely different set of categories by which to sort reflection spectra. Two objects which we classify as the same color, they might consider different, or vice versa. But, if those aliens wanted to facilitate communication with us, they might hook up a spectroscope to a computer, and program the computer to reliably tell them what color we would consider the object. “Brown” might then be defined as “having a reflection spectrum which the color-meter identifies as brown”.
I feel obliged to point out that Cecil has already covered the question of “brown-ness” in Why is, um, fecal matter brown?
Well, OK, maybe he didn’t, but I couldn’t resist.
Why do cats purr? Why do Cheshire cats grin? (09-Apr-1976)
http://www.straightdope.com/classics/a1_007.html
Let me give this a try 
Colors do not exist “out there”. Frequencies, or packets if you will, of energy are out there bouncing around, some being absorbed and others being reflected by various objects they hit. Some of that energy reflected from an object enters our eyes, strikes our retina, and is converted to nerve impulses that travel to the brain over the optic nerve. Now ignoring the whole mind/brain issue for a moment, the end result is that those nerve impulses arriving and being processed in the brain results in our minds having a perception of what we call a color, and we have learned to describe that perception by giving it a name (e.g. brown).
For example, on my desk I have a bottle of Diet Coke. Above my head I have some florescent lights. These lights generate all the frequencies of energy that my retina is capable of turning into nerve impulses. When I look directly at the florescent lights, and end up receiving the resulting nerve impulses in my brain, I give the perception I have in my mind the name “white”.
OK, now all these frequencies of energy generated by the florescent lights are bouncing around the room, and they hit the letter “C” in the word Coke on the label of my soft drink. The ink the “C” was printed with absorbs all of these frequencies of energy bouncing around the room except one (actually a narrow band of frequencies, but for the sake of simplicity I will say one). When I look at the letter “C”, the reflected frequency enters my eye, hits receptors on my retina, which results in certain nerve impulses being sent to my brain. The perception that results I have learned to call a color, and specifically the color red.
Now here is the fun part. You look at the “C” and that same frequency of energy goes to your retina, then nerve impulses go to your brain, and you have a perception. However, I have no idea what you perceive in your mind. Yes, you would say it is a color, and you would say it is the color red. But it is possible that what you are perceiving and giving the name red is what I, in my mind, perceive as and call the color blue.
The same is true of all the other colors. I can measure the frequency of the energies reflected, I can measure the nerves firing and the brain activity, but I cannot perceive your perceptions; and red, yellow, blue, green and all the other colors are perceptions. If there were no living things, there could still be frequencies of energy bouncing around and being reflected and absorbed, but there would be no colors. There are no colors “out there”.
As for the question of whether a tree falling in the forest with no one around to hear it, does it make a sound? It depends on your definition of the word “sound”. If by sound you mean vibrations in air pressure, the answer is yes. If you define sound as the human perception of those vibrations in air pressure, the answer is no.
That would be what I mean. And it means that, whether a human exists or not, there is something that exists to indicate that a tree fell as opposed to a tree which is still standing.
The same would be true of an object which has reflected, refracted, etc. light. As Chronos said, even without a human to give interpretation to the “color,” a machine such as a spectophotometer would indicate that different objects treat light in different ways. The differences are real. They exist. Us humans merely have the audacity to name the differences. But they are real and do exist.
Yes, I agree, the differences ARE real, and the perceptions are real too, in some sense, but whilst we can all share the knowledge that there are photons bouncing about, and we can all share the knowledge that generally when those photons hit your eye you see yellow or blue or red, we can’t share any description of what ‘yellow’, ‘blue’ and ‘red’ actually mean, that does not take the form ‘well, it’s the colour of that dish / the sky / the coke can’ or ‘it’s what’s caused by electromagnetic waves of frequency x’. These forms of describing colour simply beg the question. They are descriptions that associate with colours, sure, but there’s no actual description of the colour in any of those statements. We still don’t know what it’s like to have a colour perception of that sort by those descriptions.
So this isn’t to do with audacity so much because colour is more than the differences you describe. A spectrometer can tell you things can treat light in different ways, but it can’t tell you what ‘yellow’ is. It may be able to have some reaction to various photons smacking into it, but it’s not ‘seeing’ in the same sense we are. It could tell you what someone MIGHT see, given the additional information ‘People see yellow when light waves of 560 nanometers or whatever hit their eyes’, but it doesn’t tell you, and doesn’t know, anything actually about what it is like to see yellow. So it can tell you that you will see a colour, but it doesn’t tell you what that really means. If you don’t already know what ‘yellow’ is, you won’t have any further idea what to visualise. Plus it seems as though no description of yellow to anyone who has never perceived yellow would be adequate at all. (Contrast with squareness - if you told someone to put four equal length lines perpendicular to one another on a 2D plane so that the four lines link up to form an enclosed space, you might describe squareness, and even if you didn’t, I don’t think that it would be too difficult to refine that description until someone really did understand squareness through description alone. No matter how many times you say things about your idea of ‘yellow’, no one is ever going to be able to comprehend it.)
So the important distinction is that our way of noting ‘colour’ is entirely subjective, as opposed to giving off photons, and squareness, which are entirely objective. To see why, think of it the other way round. If colour were objective, then each photon would have to carry bits of colour around with it. But why more photons should give you a different colour remains unclear, for each photon is identical. So it seems impossible that different quantities of identical photons can ‘carry’ different colours. It must be an internal mechanism of the brain that translates numbers of photons into colours.
So it’s not that what you’re saying is incorrect particularly - it’s just that the notion of colour is getting confused with the notion of reflecting photons. When we say ‘That’s yellow’, we mean ‘that reflects light in such a way that it STIMULATES my thoughts of the colour yellow’. To put it simply: human beings make colours. Objects give off photons and such. The giving off of photons stimulates our notions of colour, but isn’t where colour is physically located.
Thus we get our conclusion that if there are no people, there are no colours. Just photons.
-James
They do.
They don’t, and they aren’t.
It is impossible, because they don’t.
No, it’s a biochemical/physical mechanism in the eye that reacts to the absorption of a photon (or packet of photons), creating an electrical stimulus (“nerve impulse”) that travels to the brain anc causes a change in mental state. This change in mental state is what you are calling “color.”
When understood correctly, the point is trivial – without humans, there are no human mental states, and no two humans create exactly the same mental state in response to the same stimulus. But to say that color is a change in mental state and nothing else is physically incorrect and philosophically confusing.
My first try at this reply got lost during preview, and now I see that I left off this part of the discussion when retyping:
“Color is a property of individual photons or their combinations, defined physically by the frequencies of their waveforms, being absorbed by the pigments in the eye. The number of photons determines the intensity of the light, not its color.”