Sunsets over industrial cities are usually dull and lack colors other than shades of red. If the region is heavily polluted, that what the new scientist journal observes..the sun appears as a dull red disc that may fade away even before it reaches the horizon.
In an exceptional clear, unpolluted atmosphere, the same journal explains, that the colours of sunset are especially vivid. The Sun is bright yellow and the adjacent sky is shades of orange and yellow. as the Sun disappears below the horizon, the colours change gradually from orange to blue. Low-lying clouds continue to reflect the light of the Sun, even after it has vanished.
This photo was taken outside our house by hubby 2years ago, and you can tell which is one i was mentioning above this belong.
Just imagine the variety of beautiful sunsets that will enjoyed in a pollution- free world!