A computing device includes an illumination sensor which detects external illumination, a processor which sets a screen design as a first screen design when a first condition is satisfied, wherein the first condition is satisfied when the external illumination is lower than a first threshold illumination value and a current illumination, which is currently stored, is higher than the first threshold illumination value, and sets the screen design as a second screen design when a second condition is satisfied, wherein the second condition is satisfied when the external illumination is higher than a second threshold illumination value higher than the first threshold illumination value and the current illumination is lower than the second threshold illumination value, and a display which displays an image on a screen thereof based on the set screen design.