In this study, the authors conducted an experiment to see how a background color of Web-based tests (WBTs) can affect the performance of Web-based test takers and their brain activities. Twenty one subjects in their twenties took Web-based English grammar tests and also performed circle-counting tasks on a computer screen with white and light blue backgrounds. Two dimensional images of hemoglobin (Hb) concentration changes in the brain of each subject were recorded by using near-infrared spectroscopy (NIRS). On average, the subjects scored higher on both the English tests and the counting tasks with the light blue background when texts and symbols were presented in black. The NIRS images obtained in the experiment showed that areas in the brain associated with linguistic tasks tended to have higher Hb concentrations for the light blue background than the white background. Also, the brain areas related to eye movements showed higher Hb concentration changes while the subjects were looking at the screen with the white background. Even though the NIRS signals were not analyzed in details, these results suggest that white color may not be the best choice for a background color of a WBT.