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?

Answer 1

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.