Information and Communications Technology (ICT) devices are increasingly become part of our daily lives because they can improve the quality of human life; these devices are even being implemented in the healthcare sector. Several studies have suggested that the design of the screen background can improve user performance. In this study, we determine whether performing difficult brain tasks on screen backgrounds of different colors can affect brain functions when using a tablet computer. Our subjects were from two age groups, and they performed reading span tasks (RST) using backgrounds of three colors: white, blue, and green. We recorded the changes in the hemoglobin (Hb) concentration in the frontal lobe of each subject by using near-infrared spectroscopy (NIRS) while the subjects were performing the given tasks. The results of the RST performance showed that the task scores were the lowest on a white background for both the young and the older subjects. The NIRS data showed that, on the white background, the brains of the young subjects were activated the least whereas the brains of the older subjects exhibited the highest activity. These results suggest that a difficult task on a white background can burden a user, and the burden can activate the brain of an older subject whose brain functions have weakened. These results can help create a suitable design for ICT devices to be implemented in the healthcare sector.