The color cyan – between green and blue – is a hidden factor in encouraging or preventing sleep according to biologists, reports BBC.

University of Manchester researchers say higher levels of cyan keep people awake, while reducing cyan is associated with helping sleep. The impact was felt even if color changes were not visible to the eye.

The researchers want to produce devices for computer screens and phones that could increase or decrease cyan levels. Sleep researchers have already established links between colors and sleep – with blue light having been identified as more likely to delay sleep.