Is a Color Just a Wavelength of Light?

This is such a broad topic that I will not even try to give a broad overview of it. Here we find ourselves around the neighborhood of a perennial debate in philosophy that began with Plato and Aristotle. It is the debate about if properties, if they exist, are "universals" (multiply exemplifiable and nonspatiotemporal, see below).

So far I'm learning in metaphysics that I am what is called a "realist", I believe that properties (like redness) exist and that not only can they be in more than one place at the same time (they are "multiply exemplifiable") but that they are also not in space and time, i.e., they are not spatiotemporal. So redness, for example, would exist even though nothing existed that exemplified it. It would also be nonsensical to ask "where is redness?" since it is nonspatiotemporal.

But I have been pondering these sorts of properties in relation to modern science and have seen that one's theory of existence and identity will determine whether or not one is a realist as I am. Typing this up gives me another way to prepare for that crazy midterm next week (argh!).


There are two specific issues I've been thinking about:

FIRST, CONCERNING EXISTENCE:

• When we see the color red, we really are experiencing a "dialogue" between different wavelengths of light, the chemical structure of the object we are perceiving, and the rods and cones in our eyes that allow us to make sense of all this. This can be a type of "reductive analysis" of what a color really is. Well then one starts thinking, "I know things exist because they have some sort of causal chain about them." Color exists because it's really wavelengths of light that have "causal powers" that allow me to see them. Similarly, many things that we know exist are known to exist because they cause things.
  
• So we are tempted to construct a theory of existence that says, "something exists if and only if something has causal powers." Many times this "causal powers" clause will be clarified by non-realists to entail "physical" as well, since how can a non-physical thing have any causal powers?
• So it follow from this that abstract (not spatiotemporal) properties cannot exist, and neither can numbers or even the laws of logic. What are we to do with this? Are we confident that everything that exists must have causal powers or should we modify our theory of existence?
• Is it not true that something must exist before it has causal powers? Before I have the causal power to raise my hand through volition, I must first exist. Before a wavelength has the power to react with a chemical structure it must first exist. So we see that the temptation to reduce existence to causality assumes existence in the first place. It cannot itself provide an account of existence (think, "does causality itself have causal powers?").
  
• It's also very important to note that we now see that existence is a fact about an object before science says anything about it. In other words, that something exists is a metaphysical fact about an object and not a physical one described by physics or any other branch of science for that matter. The question of existence is one within the realm of philosophy, not science.

SECOND, CONCERNING IDENTITY:

• Saying that colors are just wavelengths of light also is important when thinking about identity. If something is identical to something else, "they" (as JP says, "they" really refers to one thing here) must share all the same properties. So all the properties true of Abe Lincoln will be true of the 16th president of the United States if they are identical.
• Now if colors are just wavelengths of light, it would follow that everything true of colors will also be true of their corresponding wavelengths. To be identical, they must have all the same properties. If we can find one property true of color that's not true of wavelengths of light, or vice versa, they cannot be identical.
• Actually, what we see in science is not a statement of identity concerning colors and wavelengths of light but just the observation that they occur at the same time, or in philosophy-speak, they are coextensional. One occurs, and the other is there too. Really, that's all we know from science: when there are certain wavelengths undergoing certain interactions, color accompanies that, and vice versa. An example of coextensionality is triangularity and trilaterality: they necessarily occur together but there is something true of the former that's not true of the latter, namely, it has angles. So they are coextensional but not identical (though it is tempting to say they are identical).
  
• So does it follow from the fact that colors and wavelengths of light are coextensional that they are identical? Nope. So up to this point, science has not really told us anything about what color is, just what causes it (see above) and what "accompanies" it. From these it does not follow that color is identical to wavelengths of light.
  
• Moreover, I think we can find things true of color that are not true of wavelengths of light. That would then require a realist defense of properties that I won't go into here. But if true, it would definitively demonstrate that colors are not identical to wavelengths of light.
  

Any thoughts?