Black box should be cheaper. Those are "roto bass" strings. No silks.
The blue pack should cost a little more. the nickel/nickel plated variant of Swing Bass 66. Beer can blue silks.
The Jury is out on whether or not they are actually the same string. I've had both, but not back to back.
I've used the blue kind several times and they are probably my overall favorite nickel/nickel-plated string. Roto just R&D barky, punchy sound like nobody else.
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