Veronica Shirley Blue The blue in the front and in the old lavendar pot
Everyone loves Virginia Bluebells (Mertensia virginica) for their sapphire blue flowers on 18in stems that gleam from shady spots in April and May.
How to grow Russian sage @ The Telegraph
wall-flowers. leave holes in stone wall for hidden flower planters
Phlox divaricata 'Blue Perfume'
Alchemilla mollis and Geranium 'Johnson's Blue'
Mottled silvery leaves with stunning deep-blue flowers in Spring. The leaves are a lovely shape. This would be good in the gaps under the Acer, and all along that bed.
Scabiosa columbaria No, it isn't a spell, tho it's somewhat spellbinding. http://thegardengeeks.net/plant-guide/1950-scabiosa-columbaria GardeningGeek