• Indigo

• Wavelength: 420-450 nm
• Emotion: sadness
• the deep blue of twilight and deep water — the threshold between day and night
• evolutionary signal: fading light, reduced activity, seasonal change, introspection

• properties

  • low arousal, low energy — induces contemplation and withdrawal
  • the color of dusk, the transition into darkness
  • historically the most expensive dye — extracted from Indigofera plants

• in nature

  • twilight sky: the signal that activity must cease, predators emerge
  • deep ocean: below the photic zone, where light cannot reach
  • winter sky: seasonal affective response — less light, less serotonin, inward turn

• in prism

  • inactivity, declining metrics, dormancy, deprecated content
  • the quiet signal — something fading, needs gentle attention