Okay, when I was in about 6th and 7th grade, I read a collection of books that would be considered maybe older children fantasy/adventure. I don't remember too much about them, but will try to type what I do remember. There were a few kids in the books. They all had different colored gems/jewels/stones (I don't remember what they were exactly). These stones did different things. I do remember the boy having a red one, the girl having a purple one and another kid having a yellow one. In the books, there was a witch and some other creatures. Beyond this, I don't remember much at all. Is there anyone that can help me with an author or title to one of the books or anything? Thank you so much!