In the natural world, too, colors which sit beside yellow on the spectrum mix with it to create putrid shades that bring to mind acid, pus, poison, and toxic foods and flowers, causing revulsion and fear. Shakaila Forbes-Bell, fashion psychologist and founder of Fashion is Psychology, notes that it’s the color most associated with urgency and alertness. “Having a greater effect on attention compared to cooler colors like blue and grey, yellow has been proven to induce feelings of high arousal which activates the ascending reticular activating system (ARAS) in the brain, leading to increased heart rate, blood pressure, mobility and readiness to respond,” she explains. Think of the use of yellow in everything from road signs and horror films (Kill Bill, we’re looking at you) to graphic designer Harvey Ball’s 1963 smiley face, later adopted as the symbol of rave culture. What gets hearts beating faster than ecstasy and two-stepping?