Radio waves, x-rays, radar and light are all electromagnetic radiation. What makes light visible and others not is simply the sensitivity of our eyes. Radiation is defined by wavelength.
Imagine moving along the scale of radiation from long wavelengths (which includes radio waves) to short. Leaving radio and radar far behind, we come to infrared, which is given off by hot things. Wavelengths that are short than this just become visible, as a deep red. A little shorter again, we see orange. Shorter still is Yellow, then Green, then Blue, then Violet. After Violet, the radiation become invisible once more, it is ultra-violet.
Visible wavelengths are the colours of the rainbow. More particularly, they are the colours of the spectrum. Sunlight contains all of them (Plus some of the invisible radiation like infra-red and ultra-violet). White light is the result of mixing all of these colours together, and this is what our eyes do.
Sunlight is out standard not only for brightness, but for colour. In the middle of the day, it seems colourless, we usually call it White light, because we are so you to it. Colourless/White is, simply, normal. Even so, our eyes are more sensitive to some colours than others.
Light becomes colour, when some part of the spectrum is missing. Daylight normally becomes coloured in just two directions.
On a clear day, what happens to the colour of the sun as it sets. Much depends on the weather, but usually, as it starts to get lower in the sky, it becomes yellow, a little lower it becomes orange. In the best of sunsets, the colour is red by the time it reaches the horizon.
The reason for this is that all the particles in the atmosphere scatter some of the light and there is more atmosphere between you and the sun at sunset. The scattering, however, is selective. The shorter wavelengths get scattered more easily, leaving the longer ones visible. It is the blue that gets scattered, so that what remains looks orange or reddish. This same scattering makes the sky away from the sun look blue. You are therefore looking at the wavelengths that have been scattered. In shade on a sunny day, the light comes from the blue part of the sky.
The possible colours of daylight can be laid out on a scale that goes from red, through orange, straw coloured, white, to blue. This is important in colour photography because there are times when you will not want coloured daylight.
Chantelle Grace Photography 