The Shizhuzhai Shuhua Pu is the oldest color printed book in the world! This book of illustrations was printed in China in 1663 by the printer Hu Zhengyan, who used a revolutionary technique for the time, the polychrome xylography, invented at the end of the Ming Dynasty. If this technique was already used for single prints, this is the first time that a full book is printed in color.
Shizhuzhai Shuhua Pu translates as Ten Bamboo Studio, Manual of Painting and Calligraphy, and the illustrations it contains are simply beautiful. These images are from the Cambridge University Library, and I also recommend the posts Download more than 2500 vintage Japanese prints in HD and The first coloring book from 1760.