Pyschologist Helen Irlen, author of the book
If you choose to have your child evaluated at an Irlen Center, your child will first be screened to determine whether reading improves with use of a colored overlay; if this seems to help, your child will work with a diagnostician using a wide array of colored lenses to determine the precise color that seems to work best for your child.
You can also achieve some of the benefits of this approach by buying colored overlays from an art or theatrical supply store for your child to use. Although this is not as precise has having your child evaluated at an Irlen Center, it may afford some relief.
Keep in mind that the Irlen program is aimed at addressing a particular problem with vision; it may help your child comfortably focus his eyes on a page, but this program does not address other symptoms of dyslexia or include strategies to teach reading. This approach is probably best used in combination with other educational therapies.