• Red

• Wavelength: 620-750 nm
• Emotion: anger
• the longest visible wavelength. highest energy in the warm spectrum
• evolutionary signal: fire, blood, thermal injury, dominance display

• properties

  • highest arousal of any color — accelerates heart rate, increases blood pressure
  • most visible at distance in natural environments
  • the color of iron oxide — rust, soil, Mars

• in nature

  • warning coloration (aposematism): toxic frogs, venomous snakes, poisonous berries
  • ripeness signal: fruits shift from green to red when ready for dispersal
  • blood: the universal marker of injury and vitality
  • fire: the oldest human tool and oldest human threat

• in prism

  • danger, critical failure, system overload, resource depletion
  • the stop signal — immediate attention required