- This text is part of the Superphonics series of graded readers which use a phonic approach developed by reading expert Ruth Miskin. There are four levels in this series; Blue (the easiest), Green, Purple and Turquoise (the hardest). Each level is linked to one of the core Superphonics books. Green storybooks practise the sounds taught in Supersonics Book 3. The Zebrapotamus focuses on the following sounds: double consonants, for example ll as in hill; blended consonants, for example ng as in long; and two or three consonants together, for example gl as in glad and nd as in band.