This color heightens our physical reactions. Seeing it causes people to react faster according to a study in the journal Emotion. We react to red because it is an ingrained signal of danger. Most people aren’t aware of the reaction and it doesn’t last long.
Color perception is subjective. The color I see my not be the same color you see. Probably the hardest concept to grasp about color is that color is all in your head. It’s a sensation, just like touch. Like any other sensation it’s caused by physical reality. But it doesn’t have any physical reality of it’s own outside your body. Color is not a property of what’s causing the sensation. In other words, grass is not green and the sky is not blue. Rather, they have physical properties that make you perceive green and blue.