I was browsing, and found this gem, which has distinct hues of pink and purple. I am curious so as to how the photo has shades that it has. Was it edited later? Do such colors really occur while the sun sets?
From the looks of it there is also a bluish cast to the ground on the bottom of the photograph so I wouldn't be surprised if they used a blue graduated filter inserted so the darkest part of the filter was at the bottom of the frame. Likewise, a red graduated filter would also make the sunset more intense and could be inserted such that the deepest red is at the top of the frame.
Looking though the other photographs in their gallery I notice that the color schemes to keep appearing so it is unnatural that they are all naturally occurring sunsets and in one of the photographs he confirms that he uses Lee filters when he takes the photographs.
The sunset colours are due to Rayleigh scattering, which is when particles in the atmosphere scatter certain light so it doesn't reach you. When the sun is high in the sky the particles scatter red wavelength light, leaving blue and hence the sky looks blue. However during sunset and sunrise the blue is scattered due to the different angle of the light and the length it must travel through the atmosphere to reach your eyes, thus the light looks more red during sunset & sunrise.