As I understand it, lime is usually the last colour in the book bands. I can't find much online that goes past lime and the ones I do aren't quite true to what DCs school uses. After lime they have grey, burgandy, light blue, brown, yellow then black which DS says is free reader. They also have a chart up which shows what SATS level the book band corresponds to (eg, DS is on brown which says 4C next to it).
Some of the books in the vast free reader section are easier than the book band ones DS reads (and look far more interesting!) so I am quite keen for him to get past bloody book bands and just read what he wants. He is quite an avid reader anyway and has seen quite a few in the free reader section he wants (Tom Gates etc). I don't understand why our school has so many random book bands when most schools seem to just stop at lime. It can't be the only school that does this can it?