First, take a look at Question 2384 and its answers, which are closely related to your question. Your question is related to what is called the "inverted spectrum", a philosophical puzzle posed by John Locke, one version of which is this: Is it possible that objects that have the color you describe as "red" are seen by me as if they had the color you describe as "green", even though I also describe them as red, and vice versa? Posing the problem is difficult; e.g., objects arguably don't "have" colors, but reflect light of certain wavelengths, which are perceived by us as certain colors. "Is the color that I perceive as, and call, red the same as the color that you perceive as what I call blue?" is another way of posing the puzzle. Part of the problem is that there doesn't seem to be any way to decide what the answer is (if, indeed, it has an answer). What experiment would decide between these? Perhaps such color-perceptions (more generally, what are called "qualia") are such that a functionally complete theory of the mind (or brain) would not enable us to distinguish between them. For more on this, see the Stanford Encyclopedia of Philosophy article on "Inverted Qualia".

There are two different, but related, issues here, on neither of which is there universal agreement among philosophers (but, then again, is there ever?).

First, there's "Molyneux's problem": Can a person born blind who later gains sight distinguish a cube from a sphere merely by sight (assuming the person could distinguish between them by touch)? There's some empirical evidence that the answer is "no". The psychologist Richard Gregory has investigated this.

But closer to your specific question is the philosopher Frank Jackson's thought experiment about "Mary", a color scientist who lives in a completely black-and-white world but who is the world's foremost expert on color perception. She has never experienced red. Would she learn anything if she experienced it for the first time? I.e., is there anything "phenomenal" to the experience of red over and above what physics can tell us? Jackson originally argued that there was, i.e., that Mary would learn something from the experience of red, namely, what it's like to see red, but he has recently changed his mind. The novelist David Lodge has explored the Mary story in his novel Thinks....

For more on Jackson's thought experiment, see the anthology edited by Peter Ludlow, Y. Nagasawa, and D. Stoljar, There's Something about Mary (MIT Press, 2004).

Do you think that colours emitted by neon gas have a particular neon quality? I'm not sure. But your question could very well be asked of the metallic colours, such as silver and gold. They are not "made" by any combination of primaries, so how are they made?

There are objective scientific tests which show that we don't all see colours the same, such as the Ishihara test for colour vision. Most people don't even see the same "colours" out of both eyes. For many people the left eye might see things more saturated than the right.

The question should also perhaps be refined a bit. Shouldn't it be formulated as whether we see things (objects, surfaces, volumes etc.) in the same colours? "Do we see colours the same?" as it stands seems to mean, "Do you see red as I see red?" But this presupposes that we are both seeing red, and then the question seems to ask whether we see it the same way, for example with the same degree of saturation or exactly as blue.

This is a much discussed question, which often appears in the guise of the "inverted spectrum hypothesis": One might wonder whether some other person sees what you see as red the way you see green, etc. It turns out it can't be quite that simple, but one might nonetheless wonder whether we do all see colors the same way.

In fact, Ned Block has argued that there is some empirical evidence that we don't all see colors the same way. (See this paper.) It goes without saying that this is very controversial.

This is one of the issues that perplexed Wittgenstein in his work on colour. The fact that there just seem to be the colours that there are looks like a synthetic a priori proposition, necessary in some sense, but describing matters of fact. Yet colours have often been taken to be good examples of what empiricist philosophers called secondary qualities, features of reality that may be experienced in different ways by different people. How then can we lay down as a rule that there will be no other colours? Wittgenstein argues to a degree that we have this colour system and it is fixed in the way it is right now, and so thinking about new colours does not really make sense within the framework of that colour system. But then he also argues that we could not make sense of the idea of people going to the moon, given our system of physics, and not only can we make sense of this, it has even happened. It rather depends on whether you think that our colour system is an interconnected network of meanings that cannot be broken or changed without radical alteration to what we mean by colour itself, or whether you think it is more like a scientific system. What is fascinating about colour is that it seems to be both, something that Wittgenstein invites us to reflect on.

Neon red is simply red light emitted from an enclosed clear transparent vacuum tube containing the element neon, to which an electrical current is applied. Neon actually emits a red-orange color. Other colors can be obtained by introducing other gases in the enclosure and also by changing the color of the tube. What you may be asking about is the distinctive glow emitted from a neon tube. The red of a neon tube appears different from the red of a painted surface, for example. Different materials emit or reflect red light in different ways, and our visual system is sensitive to many of those differences.

I think you've pretty much answered your own question. You see (get it?) that light could exist even in the absence of any creatures sensitive to it. And of course in such a situation, there would be no one and nothing experiencing the light. So is anything visible? "Visible," like many English words that end in "ible," "able," "uble," or "ile," picks out what philosophers call a "disposition" -- a condition of being ready, so to speak, to cause certain things to happen, or to undergo certain changes, if certain conditions are met. Salt is soluble -- that means that if it's put into a pot of water, then it will dissolve. Waterford crystal is fragile -- if you drop it, it will break. Similarly, to call an object visible is to say that if it is illuminated, and if a creature that is sensitive to light points its sensitive parts toward the object, then the object will cause the creature to have visual experiences (by bouncing the light onto the creature's eyes in a particular pattern).

The thing about dispositional properties is that objects can have them even if and while the "activating" conditions are not being met. The salt is soluble even while it's sitting in the carton (that's why you want to store it in a dry place -- if it weren't soluble, it wouldn't matter.) And the Waterford crystal is fragile even while it's sitting on the dining table (that's why you need to be careful with it. In fact, best not to use the good crystal at all.) Similarly -- and here comes the answer to your question, finally: things in the universe can be visible even if there's no one around for them to cause visual experiences in.

Now you wanted a little science, so here's a little science. It's an interesting question, part scientific, and part philosophical, whether color is a dispositional property of things. It turns out that color perception is amazingly complicated, and that it is not just a reaction to or detection of simple physical property. The physical property of objects that comes closest to being the objective basis of color is "spectral reflectance" -- a dispositional property of surfaces to reflect incident light in different patterns of wavelengths. But there are different combinations of wavelengths that will be perceived by human beings as the same hue. So what's color? Is it just the dispostional property of producing the effect of color perception in human beings (or other perceivers)? But in that case, the set of physical structures that have the property of being, say, teal is not going to be picked out by some objective physical property they all share, but rather by reference to the "teal-effects" they produce in us. That's different than the situation is with light, and it's lead some philosophers to conclude that color is really in the eye of the beholder. I think that view is wrong, because I think a set of physical structures still has something objectively in common if they all have a common power. But there's a lot of disagreement about this whole thing.

If you'd like to learn the details of the color debate, as well as some serious color science, here are two recommendations for further reading: the entry on "Color" in the Stanford Encyclopedia of Philosophy: http://plato.stanford.edu/entries/color/ and a book called Color for Philosophers by C. L. Hardin.

One might say that a person causes the property kind to be instantiated when she decides to perform a kind act: She causes there to be a kind act.

But we cannot really say anything like this about static objects. The stone does not cause heaviness to be instantiated, the relationship between stone and heaviness is too close for this. Something heavy comes into existence together with the stone. The stone does not cause its own existence, so it does not cause the instantiation of the property heavy.

Now a tomato is unlike a stone in that it changes (its color turns from green to red) and also unlike a person in that it does not make decisions about how to be. The latter discrepancy seems to me less significant when we are speaking about causality. Considering a tomato plant we can, I believe, say both that it causally produces fruits that eventually mature to the point where they are red (thus causes the property red to be instantiated) and also that it instantiates this property (when parts of it are ripe fruits). I feel less confident about saying this about a tomato that matures on your window sill. It instantiated green yesterday. It instantiates red today. But we would be inclined to say that processes in the tomato, not the tomato itself, (together with external factors such as warmth) caused the change in color. This inclination, however, may be a mere convention: Changes in persons and tomatoes can be caused by processes within them. And there seems to be no deeper reason why we should be prepared to say in the first case, but not in the second, that the change in X was caused by X.

I suspect the point of this question was to see whether you could articulate the idea of a "category error," that is a statement that is syntactically correct but is nonsense because its predicate cannot meaningfully be attributed to its subject.

If this is what the interviewer had in mind, your answer was essentially correct but could have been stronger if you had explained that this was one example of a more general problem. If your interview was at an Oxford college, you probably would have earned bonus points if you had referred to Gilbert Ryle's classic discussion of category errors.