Paul,
I did some additional digging on the Ford engine color for the 1951 F1, and this is what I discovered:
"Engine Colors:
Ford engines were generally dark blue in 1949 and changed to bronze in late '49 production through 1951. For 1952 and 1953 the Ford engine was either tangerine red or green. The Ford truck engines were red from 1948 through 1951, and then changed to green for 1952-53. 
Mercury engines were green in color from 1949 through 1951. From 1952 to 1953 they were either green or tangerine."
This will muddy the waters a bit more:  
Ford Engine Colors So, going by the list, I'd go with either Bronze or Green for a 1950/51 Flathead Ford V8 instead of the Ford Blue.
Jim