A previous study of the effects of background colors on the scores of a computer-based English test indicated that a combination of black text and a background color with high luminance and high brightness, such as white or yellow, was not considered preferable for computer-based tests (CBTs). In this study, the authors conducted an experiment to see how a background color can affect the brain functions of CBT test takers by observing relative changes in hemoglobin (Hb) concentrations in their brains by using near-infrared spectroscopy. In the experiment, seven male subjects in their twenties took computer-based English tests with different background colors with black text. Two dimensional images of the Hb concentration changes obtained in the experiment showed that areas in the brain associated with memory retrieval tended to have higher Hb concentrations while the subjects were taking the tests with blue backgrounds. On the other hand, areas in the brain related to other functions, such as the frontal eye field, were observed to be more active than brain areas responsible for cognitive tasks while they were taking the test with white background. These results suggest that white color may not be the best choice for a background color of a CBT, in terms of activating brain functions associated with linguistic tasks, even though a white background is commonly used for CBTs.