It's a very interesting topic because many people assume that the solar spectrum is very even across all wavelengths. This is reasonably accurate in the vacuum of space but the earth's atmosphere will absorb certain wavelengths based on it's chemical composition and density or thickness. We see the effect of this as colour temperature shifts (morning, midday & sunset for an example of the atmosphere thickness affecting wavelength absorption) but there is more subtle effect where certain wavelengths are reduced by the elements in the atmosphere absorbing the sun's radiation in selective bands in different amounts depending upon the atmosphere's thickness, (as illustrated by Vitaliy) resulting in certain colours being mis-represented when compared to a midday sun, even after being colour corrected.

Colour spectrum research on artificial light sources is very interesting for film makers as it can reveal the reasons why certain light sources (sodium street lamps for example) are more difficult to correct than others.