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.