Pink Level
These are phonically decodable in the main. Usually one short sentence per page. Illustrations give vital cues to the children.
Yellow
Yellow books are use phonics from phase three. They have a wider selection of the "tricky words" and more words on a page. We could expect children to be reading at this level by the end of Foundation Stage.
Green
Green level books have a much wider selection of CVCC words and once again more text on a page. The subject matter is often more advanced as well.
Orange
This is around the typical level for Year 1. Some children will be reading at a higher level and some at a lower one. Orange books are longer and require more reading stamina. In addition, they require more complex phonics to decode them and there are more tricky words to recognise. This level is about children reading with real fluency and understanding.
Turquoise
These text are much more complex and generally children can decode fluently by this point. Comprehension is very important at this point and turquoise books have a much wider variety of genre.
Lime
This is usually the level for able Y2 children. They are often short chapter books with fewer or no illustrations.