I read this book in the mid 90's, probably between 95-98. It was a picture book targeted at probably K-2. It was on the larger/taller size and it had a gray brick castle on the cover and a lot of the illustrations were of the castle. The characters were a young princess with long red hair and her friend who was a boy with blonde hair and freckles. They got into mischief together, led by her I believe. Most of the book was about the two of them playing together in the castle. The illustration style was clean and sharp, somewhat realistic but simplified, and more 3-d-ish than flat. . . I remember images where they were on upper levels of the castle and the girl was closer to the front, the boy farther away. I believe it might have come from my school book fair, so it was possibly Scholastic.