The radiation curve of the sun shows that the brightest light fro the sun is yellow- green. Why, then, do we see the Sun as whitish instead of yellow green?

The emission curve of the sun is reasonably flat from blue (500 nm) to orange (620 nm), but it is true that it does peak in the yellow-green (550 nm). The eye responds to radiation in three overlapping broad bands. Sunlight stimulates all three bands. The color perception of the human eye and brain depends upon relative amounts of color in those bands, as well as other factors, such as overall light level. (For example, the brain tries to compensate when objects are illuminated by sorces colder than the sun, such as incandescent light bulbs, by making things look whiter than they are.)

The daylight mix of signals from the sun is perceived as white, almost by definition. It's how the brain works; to try to explain it better would require more physiological optics than I know.

We see the Sun as whitish instead of yellow-green because of a phenomenon called the additive color mixing. This phenomenon occurs when different colors of light are combined to create a new color. In the case of the Sun, it emits light of various wavelengths, including those in the yellow-green spectrum. However, when these different colors of light reach our eyes, they mix together and create a perception of white light.

To understand why this happens, we need to consider how our eyes perceive color. Our eyes have three types of color receptors, called cones, that are sensitive to different ranges of wavelengths: red, green, and blue. These cones send signals to our brain, which then interprets the combination of signals as a specific color.

When we look at the Sun, the cones in our eyes detect not only the yellow-green light but also other colors emitted by the Sun, such as red and blue. These three primary colors of light (red, green, and blue) trigger a mixed response in our cones, which our brain interprets as white light.

In simpler terms, even though the Sun's radiation curve peaks at yellow-green, our perception of its color is influenced by the combination of colors emitted by the Sun, resulting in a whitish appearance.