“Feeling blue” might be more than just a metaphor. Indeed, how we feel about the world can play a huge role in how we see it, according to a new study in the journal Psychological Science. Feeling sad can keep us from seeing in certain colors, as though we live in Dorothy’s Kansas. But a good mood can bring those colours back into the world, just like a tornado trip to Oz. “We were already deeply familiar with how often people use colour terms to describe common phenomena, like mood, even when these concepts seem unrelated,” the study’s lead author Christopher Thorstenson said in a statement for the Association for Psychological Science. “We thought that maybe a reason these metaphors emerge was because there really was a connection between mood and perceiving colors in a different way.” Thorstenson was right. All it took was a clip from a cartoon to make people start seeing differently. Participants in the study, which took place at the University of Rochester in New York, were invited to watch the two-minute scene from “The Lion King” in which heroic Mufasa is killed. To the mournful strains of Elton John’s score, they watched Simba’s eyes widen and fill with tears as he nuzzled against his fallen father. The clip - which apparently is often used in psychology studies - is scientifically proven to induce irresistible sadness at the plight of the orphaned lion cub. Others participants were shown a clip from a stand-up comedy routine or a neutral screen saver. Once they felt sufficiently gloomy, cheerful or completely unmoved, depending on which clip they saw, the participants were put to the test. Each was presented with a series of washed-out colour swatches, so de-saturated they were nearly gray, and asked to identify what colour they were. While the amused and neutral groups’ ability to discern colors remained unaffected, the Disney-watching crowd had trouble distinguishing swatches on the blue-yellow axis. (The eye’s colour encoding matrix ranks light on two axes — from red to green and from blue to yellow — and then sorts it into what we recognise as colour.) That only blue-yellow perception was affected, and only among the sad group, is significant. Psychologists believe that perception along the blue-yellow axis is linked to the neurotransmitter dopamine, Thorstenson told the Association for Psychological Science. Dopamine is the chemical signal that transmits information from neuron to neuron, stimulating the pleasure and reward centres of the brain. Thorstenson’s study suggests that sadness affects dopamine’s other tasks — among them, transmitting visual information about blue and yellow light. A similar phenomenon has been found in patients with ADHD, who have low dopamine levels and sometimes struggle to perceive the color blue. “Our results show that mood and emotion can affect how we see the world around us,” Thorstenson said.