Because this copy features this exact wording combined with "Typography by Atha Tehon" and no copyright page number line, you are holding a vintage 1960s book block that was bound into a later casing or paired with a later jacket bearing the 394-81011-2 ISBN.
During the mid-to-late 1960s and early 1970s, Alfred A. Knopf and the Junior Literary Guild utilized this multi-material binding to save on production costs while keeping a premium look:
To a book collector, having the "skin is almost black" phrasing makes this a highly collectible unrevised state. When Roald Dahl revised the book in 1973, these exact sentences were completely erased and replaced with the description of "rosy-white" skin and "golden-brown hair". 
This 1964 copy of the book features the original text layout on page 73 before it was rewritten in 1973. Combined with the 6-line colophon and 9-digit SBN, this indicates an intermediate printing from roughly 1968 to 1971, which collectors highly value for retaining these original attributes.