Natural white light is composed of multiple wavelengths that the human eye recognizes as differents colors. When passing white light through a prism, it makes visible the different colors that light contains. Thereby obtaining a continuous spectrum. This is the phenomenon of chromatic dispersion.
If the first third of the spectrum is focused to a point with a lens, the color perceived by the eye corresponds to blue. The middle of the spectrum corresponds to green and the third period corresponds to red. These three colors are the three primary colors of the additive synthesis. When they're supersposed, they give a lighter color. Thus, the mixture of blue and red give a magenta. Red and green give yellow and the mixture of blue and green give cyan. The mixture of the three colors produces white. It is on this principle that video screens operat, for example.
The sunlight is more or less diffracted as it crosses a more or less layer of Earth's atmosphere. Thus, it seems warm at the time of sunrise and sunset (the sun atteignants land with an acute angle) while it is rather cold during the day (when the rays are perpendicular).