Mike, Two of my 1979 D4E SAs had the old Cat yellow originally.Theother four of my D4E SAs from 1980 to 1986 are the new Cat Yellow. The D5B SA is the new Cat yellow. The D4s get painted every two years because the new paint dosnt seem to hold its shine like the old Cat yellow did. I looked at one of my original brochures from the early D4Es ( 1979) seems to have more of orange look to it. But to answer you question I think the color change was in the early 80s. according to the D4E/D5B/D6D brochures I have .