What visual color contrast characterizes the transition from the western horizon upward during Nautical Twilight?

Answer

Deep oranges/reds at the horizon shifting to deep, almost indigo blue overhead

The area near the horizon retains warm colors because that light has traveled through the densest atmosphere. Higher angles transition to deep blue as they catch light scattered from higher, less dense atmospheric layers.

What visual color contrast characterizes the transition from the western horizon upward during Nautical Twilight?
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