180º to the sun is where you will find the strongest sunset and sunrise colours. It is where you will experience the earth shadow at its strongest. Earth shadow is the blue (twilight) region in the sky, as can be seen in this image shot on my iPhone tonight on the Salar de Uyuni.
As the sun drops further below the horizon so the earth shadow heightens, until the entire sky is in twilight. In my iPhone image below, the earth shadow has just begun.
