Changing the background colour on which people are reading has been shown to effect reading ability. For this reason all of the books published by phonic books are printed onto a cream background to reduce the contrast between black and white which can cause problems for some children. Google have actually changed the colour of their search boxes based on similar results that they have found from testing which google search designs are most effective (based on live comparisons (A/B testing) of the effectiveness of different versions of the Google website).
In the mid nineties Wendy worked as a research assistant for Arnold Wilkins at the Applied Psychology Unit in Cambridge. She learnt how carry out the tests and did countless tests on children as part of the research project. For a small percentage of those tested it made a huge difference. They reported that the text no longer moved and reading was considerably easier.
Arnold is still working in this area and has an excellent page on the use of coloured overlays HERE. Coloured overlays are a much cheaper way of creating supportive reading environment than the coloured lenses that are promoted by some opticians. He also gives a useful link to some shareware software that allows you to adjust the colour of your screen to the right colour.