The book "Original Allis-Chalmers, 1933-1957" by Guy Fay covers that in some detail-sadly I don't have a copy-my dad dose but I'm on the opposite end of the country from him.
I've also found these two B&W photos in my search for tractors on flat cars, as my other hobby is model trains. The Soo line photo is from 1948 and of WC's-looks too me the rear rims are a light/sliver color, and the fronts all Orange. The other, was noted to be 1950, making it WD's. Again rear rims look to be light/sliver in color. Harder to tell, the fronts may also be all orange.
Now, It looks to me the B you show with sliver front rims has the riveted together 1-peice rim, like the WC/WD/WD45. Being one piece, I could see it to be all orange-they wouldn't take time in the factory to carefully paint in two colors, on once piece, or at least that's my logic. The other, looks to have the two piece rim-that would be easier to have orange centers, and sliver rims.
Last variable is, its been often discussed, that rims weren't painted, but still sliver in color, so that now the easiest way to capture the look now is sliver paint. And then, some say it change from year to year.