Pink Sky

Pink skys exist because of dust, water, pollution, or other things in the atmosphere that scatter red light. The pollution in the atmosphere, much of which is iron and other industrial byproducts can present shades of red when the sunlight passes through the atoms of the pollutants in the atmoshpere due to the fact that every element's atoms emit a different wavelength of visible light when its electrons are struck by energy(sunlight) as they return to ground state. The reason the skies have very warm colors during sunset and sunrise(appropriate angles for sunlight to reflect the pollution in the atmosphere) in Hawaii and the surrounding region is due to the massive pollution amounts wafting over from China.

"Red Sky at Night...Sailor's delight

Red Sky in the morning...Sailor Take Warning"

This is an old maritime way of gauging the weather. The saying is quite likely to have been passed on by word of mouth for some time before it was ever written down. There is a written version in Matthew XVI in the Wyclif Bible, from as early as 1395:

"The eeuenynge maad, ye seien, It shal be cleer, for the heuene is lijk to reed; and the morwe, To day tempest, for heuen shyneth heuy, or sorwful."

Sunlight is broken into the familiar rainbow spectrum of varying-wavelength colours as it passes through the atmosphere.- The blue/violet end of the spectrum is diverted more than the red/orange.(This is the same mechanism that causes us to see the sky as blue incidentally, but that's getting rather off our point) - When the sun is low in the sky, at dawn and dusk, sunlight travels through more atmosphere than at other times of day. The red wavelength is better able to go on a direct course and be reflected back off clouds, whereas the blue light is more scattered before reaching the cloud and is therefore less visible. So, we see the clouds as red as the light that is reaching them is primarily red.