They're different cultivars...and there are at least two more blue cultivars as well; 'Blue Heaven' AKA MinnBlueA and 'Aldous.'

'Prairie Blues' and 'Aldous' can be successfully grown from seed, while the other two are less cooperative.

'Blue Heaven' AKA MinnBlueA is the tallest and most erect in habit.

All 4 are different shades of blue, ranging from blue/green ('Aldous') to steel blue/burgundy ('Blue Heaven').

Interesting- thanks. Picked up 'the blues' in 1 gallons to plant in a group as a tall groundcover in front of rudbeckias and coneflowers. I'm hoping it looks natural and not too tacky and out of place. I like how they are only slightly blueish.