Coming back to the Blu Alfa blues: I haven't come across much information on dark Alfa blues of the late '50s and early '60s. Tech. Bulletin 0.00.024 dated 10-Jul-1961 gives an overview of the standard paints available for each model of ehat I suppose were then current production cars (relevant pages copied below and also posted elsewhere). I call these "standard" colors because undoubtedly other colors were available as well.
The only dark blue in this list is for a Giulietta Sprint Zagato (AR 328, KF 18018) but I never found any reliable information about this 'old' color. Several newer colors exist the same AR code: Blu Zagato (1970-71), "Azzurro Olympo Met" (1986-89) and "Blu Mare Met" (1987-93). I know the Blu Zagato used on the Junior Z is a medium blue, not a dark one.
The other period blues (sorry, I can't resist using this expression) like Blu Tornado, Bluette and Blu Cobalto are also considered to be 'medium'.
One of the darker blues you may want to look into is
Blu Posilipo shown in the 1972 color chart. This color obviously won't look right on screen.
Good luck on you quest -- it's not an easy one but Andrew seems to be experienced, knowledgeable and of great help.