Which colour group is more effective for creating a calm and spacious sky?

Correct answer: Blue, blue-green and light violet

The governing concept is the psychological and spatial use of colour temperature. Blue, blue-green and light violet are predominantly cool colours; they generally suggest calmness, airiness and distance, which suits a spacious sky. Warm groups such as red-orange and yellow tend to feel energetic and advancing. Brown, black and red create heaviness or intensity rather than a calm, open atmosphere.