The New York Academy of Medicine has organized #ColorOurCollections, in which various member libraries take images from their holdings and put 'em online as high-end coloring-book material.
The image above is from the NYAM's coloring book itself, but there are dozens more; some of my faves include the Carnegie Hall Archives book ... 
... the William Andrews Clark Memorial Library ... 
... the University of Adelaide ... 
... the Shangri-La Museum of Islamic Art ... 
... and the Ricker Library of Art and Architecture: 
