Pepsi changed over to the single dot in 1951, I haven't been able to find a more specific date, but I would say definitely by June that year 

  Your machine may have been one of the first with the new logo. 
 I thought but can not confirm the lighter blue didn't start appearing on machines until the late 50's-early 1960's. 
Personally, I think the dark Pepsi blue would look good on your machine, and I'll  keep my eye out for a 12"  cap decal.