Yamazaki's studies and our previous study indicated that a combination of black text and a white background color was considered less preferable for web-based English tests, comparing with a combination of black text and a blue background. In this study, the authors conducted an experiment to see how white and blue background colors can affect the linguistic functions of web-based test (WBT) takers' brains by observing relative changes in hemoglobin (Hb) concentrations in Broca's Area of their brains by using nearinfrared spectroscopy. In the experiment, thirteen male subjects in their twenties took web-based English grammar tests with white and blue background colors with black text. The average WBT score for the blue background was higher than that for the white background among the subjects. Two dimensional images of the Hb concentration changes obtained in the experiment showed that areas in the brain associated with grammar and vocabulary processing tended to have higher Hb concentrations while the subjects were taking the tests with the blue background. 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 associated with linguistics tasks while they were taking the test with the white background. These results suggest that white color may not be the best choice for a background color of a WBT to assess test-takers' linguistic performance, even though a white background is commonly used for WBTs.