When I was a child, working on reading comprehension, the school I attended in the south of Britain had a series of books that gradually got harder as you progressed. The series was colorfully illustrated and had featured blue men that were dressed in kilts and other Scottish garb. They lived in a valley and went about daily chores or adventures. As the series got to the end, some of the characters were captured by a beast that lived in a cave above the valley and were shackled to the cave walls. I think I got the details relitively close, but some stuff may be a tad off (it's been 14 years since I've seen the books at least). Do you have any idea what the series is called? I'd really love to try and find copies or images from them.