Winter Twilight Sky. Reds are made by transmitted sunlight depleted in blues and greens by scattering. The blue sky is seen by the light it itself scatters. The combination of skylight with direct sunlight, reflections and absorption by clouds and the ground add yet more variety. Contrast between adjacent complementary colours makes some stronger than they really are.    Measure the seemingly intense greens in this unretouched picture - they are mostly subdued gold and olive hues.

Photo ©2003 Les Cowley