you must first determine the year your TO was made.
Ferguson must have gotten a special on paint when they were building TO's
early 1956- green/beige (most rare)
late 1956 - gray/beige
1957 - gray/beige
1958- forward gray/red
I believe on the left side of this site you can find a list of serial numbers that will tell you when your tractor was made.
all is clear, but the early 1956 models as i do not think anyone is positive as to what serial number when they changed from green/beige to gray/beige.
guess they changed when the green paint tanks ran dry and were cleaned an recharged with gray paint,
that is how we changed paint colors at my old plant.
I have attached a picture of a 1956 Ferguson 40 that is painted in the early green/beige colors.