Nib asked, and Nib — askNib's tutor — drew the answer live at a whiteboard. This is the spoken transcript; enable JavaScript to watch it drawn.
why does the sun look yellow when its light is white
The Sun isn't really yellow. From space it is a dazzling white disc, because sunlight is every color mixed together, as a prism shows.
Air molecules bounce short waves, like blue, about four times more than long red ones. Blue gets knocked sideways, so what reaches you is yellower.
At noon the Sun's light crosses only a thin slice of air, so just a little blue is lost. It looks pale yellow-white. Don't stare at it, though.
Near the horizon the light slants through up to about forty times more air right at the horizon. Nearly all the blue is scattered away, leaving orange and red.
That lost blue isn't wasted. Scattered across the sky, it is the blue you see overhead. The same bouncing makes blue skies and red sunsets.
So the whole story: white light goes in, air scatters out the blue, and the more air it crosses, the redder the Sun looks.
The Sun is white, and our own air paints it yellow, orange and red.