Photo and ephemera collector Jim Linderman suggests--or jokes, I can't tell--that the 1927 promotiocational classic, Heinz Kindergarten Book: Pictures To Trace might have provided early source material for Andy Warhol.
Who knows? Warhol was certainly a voracious a collector and appropriator of advertising and popular imagery.
In 2003-4, the Huntington Library in San Marino exhibited a huge collection of art educational materials donated by Diana Korzenik, which included the Heinz Kindergarten Books and other vintage marketing/coloring books. "Drawn to Art: Art Education and the American Experience, 1800-1950" isn't documented online very well, but the 1,400-piece collection is apparently available for research.
UPDATE: In addition to his entirely plausible explanation for suggesting a Warhol/Heinz Coloring Book connection in the comments below, Jim has expanded on what he meant--and posted more sweet Heinz scans--on DTDB.
Where Warhol Got The Heinz? [dulltooldimbulb]
"Drawn to Art: Art Education and the American Experience, 1800-1950" [absolutearts.com]
A Brief History of the Korzenik Collection of Art Education Books and Ephemera, Accessible through RLG Cultural Materials [worldcat.org]