Rather than telling them what is on the page, ask them to describe what they see. So that children do not feel singled out, you can let the whole class experiment with colored overlays. Often children who don't need them find that they enjoy having a certain color over their page. Various colors may appeal to readers because they seem relaxing or they make the words stand out more clearly. Experiment with the various colors.
Different colors work for different people.
Scientifically, it has to do with the lengths and configuration of cones and rods in an individual's eyes. NRSI sells a packet of eight colored overlays. Colored overlays will not help ALL children with sight problems.