Pretty sure it was just the paint code. Different from Chrysler's surf blue for example. One of the guys really into the history might have a better answer.
Ddaddy and 370 Hemi are correct. I think today's Dodge folks went with calling it B5 blue because that has always been the popular name for it. Well, for the last decade or more, anyway. Most of the other HIP (high impact paint) colors were referred to by their HIP names: Plum Crazy Purple, Sassy Grass Green, Go Man Go, Top Bananna, Hemi Orange, Vitaman C etc, not by their paint code. Anytime you hear of a B5 blue car, they call it just that... B5 blue (one of my faves BTW). If you ever come across a junker with the paint code 999 grab it up. That paint code was reserved for special colors not normally sprayed by Chrysler i.e. Petty Blue.
Yeaaaahhh, but you know the guy that came up with that one was giggling like a little girl while chewing on his pen, knowing that most people wouldn't notice.
From 1969 to 1973 buyers of all new domestic Chrysler cars could order their new cars with special, extra-cost paint. These are the High Impact Paint (HIP) colors.
The High Impact Paint option cost around $15.00, depending on the model. These colors can be found on everything from (then) compact 4-doors to top-of-the-line full-size C-bodies, but are most often found on musclecars. The names were as colorful as the paints.
The following is a list of the ten most popular optional High Impact Paints, along with a best-effort representation of the color scanned from original paint chips.