According to Marie Severin (1995), “[Harvey] Kurtzman colored his own art, especially on covers....”
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References:
Cassell, Dewey, with Aaron Sultan. 2012. “The Artists of EC Comics” (reprinting Severin 1995). In Marie Severin: The Mirthful Mistress of Comics. 46–47. Raleigh: TwoMorrows Publishing.
Severin, Marie (John Province, transcriber [uncredited]). 1995. “Mostly About Color.” In CFA-APA 36, January.
Biography of Kurtzman, with photo, found on the inside front cover.
Letters from Pfc. Ray Pantalena, Ronald Pering, Vic Fera, Jerry Morgan, Dan Walleck, J. Jonborgzinner, Martin L. Burns, John Plaks, John Brown, and Roger Curtis.
This was replaced by a Harvey Kurtzman illustration in EC Archives: Frontline Combat (Gemstone, 2008 series) #1.