NYC at one time operated E8 diesels with silver trucks, as evidenced by a photo of #4048 photographed new at EMD in January, 1952. As info, other NYC diesels ran with silver trucks, such as FM "Erie Builts". Both of these photos appear in New York Central System Diesel Locomotives by Edson, Vail, and Smith.
I do not know if any EMD E7's or Alco PA's ever had silver trucks, but I believe that trucks on all passenger diesels were painted silver as they were shopped, in the 1952-55 period. Supposedly, this practice ended on the NYC as it made it easier for Federal Inspectors to "black flag" units with journal or gear case leaks, although this is hearsay.