The pictures that I'm looking at appear to show them as being stainless/chrome. It appears to me that the Loewy passenger diesels and the "F3"s had body painted screens or grills, and that the freight and butterknife passenger "F7"s had stainless/chrome.
I'd love to say "fer shure" on that, but I can't.
Ed
I am in need of forum help again. Does anyone know what color the grilles were on the Phase IV F5s and F7s that the Northern Pacific used in the original Pine Tree (or Butterknife) scheme. I presume that the grilles were the darker green of the rest of the scheme but I don't know. I have been unable to find any prototype pictures to answer this question. Thank you for any assistance the forums can provide.