The Sun is white
Above the atmosphere the Sun's light is white. It looks yellow or red from the ground because air scatters the blue end of its spectrum.
The solar spectrum is close to a 5,800 kelvin blackbody. Integrated and seen by a human eye adapted to daylight, that spectrum is white. Spacecraft images that are not arbitrarily tinted show a white disc. The blue sky is the missing blue light, scattered out of the beam. What remains, at the surface, is slightly yellow. Near the horizon, with more air in the way, it is orange and red.
Never look at it to check. The colour science is settled without a stared-at retina. The same scattering is why shadows lit by the sky are blue, and why a photograph of the Sun taken from orbit, correctly balanced, does not look like a lemon.
Caveats
- At sunset the disc really is redder. The claim is about the Sun's own spectrum, not about every glance through air.
- 'White' depends on the eye's white point. Under a definition tuned to the Sun, the Sun is white by construction. The physical point is that nothing in the spectrum singles out yellow.
Sources
- 1Neckel H., Labs D.. The solar radiation between 3300 and 12500 Å. Solar Physics 90, 1984.