"One" by Kathryn Otoshi. It's a book about colors, counting and bullying. It's won 8 awards. If you're looking for a book for an 4-8 year old, check it out! From the cover:
Blue is a quiet color.
Red is a hot head.
Red likes to pick on Blue.
Yellow, Green, Purple and Orange don't like what they see, but what can they do?
When no one takes a stand, things get out of hand. Until One comes along and shows all the colors how to stand up and count.
This book is too cute!