Posted By:
Joe D.Ted,
For the Musual....
The ink that would be added to make the dark blue background is red (by red I mean Magenta).
That is how you would create that deep blue.
The fact that there already is red on the 'light blue' version means either this was a purposeful variation - or a bad magenta plate.
Perhaps when they were on press - they thought the the blue background looked too light and decided to make a new magenta plate.
If I had the cards in front of me and had a chance to examine them in person - I would definitely be able to give better answers.
I look forward to seeing you and the cards at Philly.
I will bring whatever 50s, 60s cards I have (a binder or so) to see if you think there is anything cool in there (stuff passed on to me by family).
Maybe there is a gem or cool variation in my binder 
Regards,
Joe