Why the sky is blue, not purple (and the sun yellow-red)

Sunlight, which illuminates the sky, has a wide spectrum of wavelengths, but molecules of air preferentially scatter the short, blue wavelengths. By the same token, the longer wavelengths—green, yellow, red—tend to pass straight through the air, so the color of the Sun we see is an aggregate of those colors. So when we look at the air instead of the Sun, we see the scattered, blue light—the color of the sky.

The problem is that the violet wavelengths from the sun, having still shorter wavelengths than blue, should be scattered even more. Given this, shouldn't the sky be violet, not blue?

Using the parameters of how much the blue light scattering makes mountains progressively dim as a function of their distance from the point of view, a person can actually calculate the dimensions of air molecules (or Avogadro's number, which is closely related) and get an answer on the right order of magnitude. Indeed, a spectrophotometer shows that the highest peak of the intensity of skylight occurs in the violet range.

But why do we see blue, nonetheless? The resolution of the mystery lies in our daytime vision, which happens to be eight times less sensitive to violet than to blue light.