If you/your child are experiencing difficulties following text, gets headaches when reading, jiggles in their seat when trying to focus on text or complains that the words move around they may have a form of visual dyslexia.
Some dyslexics find it easier to read text that is on coloured backgrounds rather than white. Black text on a white background can often seem to glare or even flash, making it difficult to focus on the words and causing fatigue. In extreme cases words can seem to float around the page and become distorted.
Some dyslexics find it helpful to read with a coloured sheet of transparent plastic (acetate) over a white page or a coloured background on a computer screen, while others find it makes no difference. You need to try a few out to see which colour suits you. If it makes a big difference then it might be worth being assessed for glasses with coloured lenses by an optometrist. The lenses are often a different colour to the acetate.
The theory behind this is that white light is made up of different colours moving at different frequencies. Which can cause confusion when the brain receives that information. The coloured lenses filter out the light frequencies causing the problems. Many dyslexics are even very mildly colour defective.