Ed,
May sound like a dumb question, but do you have an early release GP40 or one of the newer (DCC ready) ones?
Reason I ask is because the early Atlas China Chessie attempts were too red in the orange. The original Atlas SD7/9 made by Kato looked good, but when Atlas went on their own, they struggled a bit to get the color right. It wasn't until about the U25B that they adjusted it to a better hue.