The default black text on a white background in Windows 7 can be problematic for pupils who experience Irlen Syndrome and/or scotopic light sensitivity.
It is possible to use existing themes in Windows 7 such as High Contrast but it is preferable to fine tune the visual settings to meet the individual needs of pupils. However, it isn't immediately obvious how to change these settings. This tutorial explains how to change and customise the background settings in Windows 7.