Beautiful Plates.
Looking through my files I found and have attached two photographs showing the different looks.
Photo 1: Shows #20 in Durango on July 19, 1947. Here the number plate is very clean and shows the background as Black and the letters and number are White.
Photo 2: Shows #20 again in Durango a year later on August 20 1948. When you look at the plate the gray tone in the background dictates Red and the number gray tone is brass in color not white as indicated by the white of the Flying Rio Grande on the boxcar in the back.
Both of these photos were shot by R.H. Kennedy of Kansas City.
Hope these help.
Michael