What color is the Sun?
Short answer: White.
Long answer: Most people think of the Sun as yellow, but it only seems yellowish to us because of the Earth's atmosphere. Actually, even to us on Earth, the Sun is not really as yellow as you might think—if you could look safely at it with your naked eyes it would be quite white, especially when it's high in the sky.
If you have ever used a solar filter or eclipse glasses you would have seen the Sun looking orange or perhaps some other colour. This is just the filter colour, not the Sun's real colour. Likewise, coloured photos of the Sun from NASA and other space agencies are coloured with filters and other processing. There are various scientific reasons for doing this—mainly to make it easier to see features or to make it very clear that the photo was taken in non-visible light (e.g. x-ray images of the Sun are often shown as green)
Why does our atmosphere make the Sun look yellow? As beams of sunlight pass through the air, they get scattered and broken into their different colours in a similar way to light passing through a prism. The shorter wavelengths that make up the colours green, blue and violet get scattered more and give us the blue sky. The remaining yellow, orange and red wavelengths tend to travel straight through without getting scattered as much. The more atmosphere sunlight passes through, the more red it appears. That's why we have red sunsets.
Technically speaking the Sun's light is strongest in the green wavelength but we don't perceive the green part of its spectrum very well. For all intents and purposes we can say that the Sun is white. At least for now... in a few billion years it will become a red giant. Then later, the final part of its life will be white again as it becomes a white dwarf star.
Image credit: The University of Chicago.
Author: Dave Owen