AN Whitehead wrote that "It takes an extraordinary intelligence to contemplate the obvious."

In a similar vein, Schrodinger said, "Thus, the task is, not so much to see what no one has yet seen; but to think what nobody has yet thought, about that which everybody sees."

Most of us see color, few of us think about it very much. Helmholtz was an exception: "Similar light produces, under like conditions, a like sensation of color."

We can both broaden and tighten this last observation with a little help from Heisenberg and say that the same state vector, acted upon by the same (matrix) operator, produces the same *spectrum* of colors, sounds, and other secondary properties. Moreover, colors and sounds and so forth behave like vectors. Weyl, the father of gauge theory, gives us the go-ahead regarding color:

"Thus the colors with their various qualities and intensities fulfill the axioms of vector geometry if addition is interpreted as mixing; consequently, projective geometry applies to the color qualities."

See the admirable text on *Sensory Qualities* by Clark (Oxford) for the general situation.

I emphasized the word *spectrum *just now because, as the mathematician Steen reminds us, early on in the history of 20th-century physics, "The mathematical machinery of quantum mechanics became that of spectral analysis...," which is just this business of matrices and vectors.

Well, in a way, we have only restated the obvious: The same thing, under the same conditions, looks, sounds, tastes and feels the same.

Yet we can say this without leaving the familiar setting of Heisenberg's formulation of quantum mechanics (QM). Isn't that interesting?

Now, from a physical standpoint, it is naturally immaterial whether the relevant operator field is inside or outside our heads, and this would seem to moot the notion that color is somehow "subjective."

I mentioned gauge theory just now, which governs the symmetries of the universe, which then determine the QM *action.* Weinberg put it like this:

"Furthermore, and now this is the point, this is the punch line, the symmetries determine the action. This action, this form of the dynamics, is the only one consistent with these symmetries [...]"

Those who wish to explore the other matters discussed here are encouraged to consider the symmetries of color. As noted, color behaves like a vector, and vectors are useful in physics in large measure because they embody natural symmetries.