I have no direct answer to your question; however, an aerial photo of Ford Island taken in November '41 (Navsource) shows Lex with a very dark deck consistent with some form of staining. In addition, Shipcamouflage.com USN states that she was in measure 12 from 1941 until April '42 when she changed to Measure 21. Both include stained decks. No idea of the reliability of either source.
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Would anyone happen to know whether Lex's decks were stained blue prior to March 1942, or Coral Sea? What was her livery during that period?