It seems wrong to me to have purple "blue" flowers in 4th of July arrangements, and delphiniums will probably not be blooming yet for you then, so... are you able to grow meconopsis?

When you visit the nursery you could ask what they have in stock and go from there.

I have all of these in bloom in our gardens except the balloon flower. A combination of them would be a lovely cottage look, but probably not a formal border except for the knockout rose.

red
Maltese Cross, Lychnis chalcedonica
knockout rose

blue shades (periwinkle, violet)
bellflowers, several types
Jacob's ladder
Platycodon grandiflorus, Balloon Flower
hardy geraniums

Some poppies do well in my yard. But I've not seen the blue ones growing around here anywhere. Perhaps it's too wet for them. I think I do want to bring back red verbena.

Good idea about dropping in on a nursery now. I've had to make a rule not to buy plants faster than I can set them in the ground. But I caught up with the backlog only yesterday and am feeling the urge to head to Flower World ... :)

I have some lovely blue salvia blooming right now, got it on the clearance table last fall without identifying information though so can't specify the variety. It is a true blue and quite dark in comparison to, say, the blue star creeper that is growing underneath it. Not sure if you could call it well-mannered though - it sprawls a bit!

I was admiring the blue salvia on someone's web page--an excellent suggestion. Thanks!