Ever hear of Gentian Blue? It is a paint colour.
These are not growing in the Alps. They are gowing in full sun on the North Fork of Long Island, outside the little town of Cutchogue, reputedly the sunniest place in New York state. They are Gentiana scabra, and Jim and Joanne Glover are growing them for future sale. These were blooming electrically in their perennial border and drew me like a hungry bee. They are easy to grow but difficult to propagate, explained their nursery manager.
The mound they form is about 4" high and perhaps 18" in diameter. They will be blooming for the next couple of weeks.
I did actually find some for sale at another nursery a week or two ago, and they are planted now on a rooftop in Chelsea, and are in fact a pink cultivar (Gentian pink?...uh...); if the blue had been available then I would have snapped it up.
Look for a cultivar called Gentiana "True Blue" (the ones I saw and also bought yesterday at another nursery were grown by Sunny Borders in Connecticut). Google the flower and see what's available, where. For a sunny spot (no fewer than 6 hours of direct sun), these are stunning. Zones 4-7.
This September-sky blue is the most blessed relief from rusty chrysanthemums...