The brilliant blue Gentian asclepiadea is in flower throughout the garden. They are late flowering this year. It is a clump forming herbaceous perennial and has naturalised in the garden. The only place it has done so in the UK. It's common name is the willow gentian.
Aesculus parviflora (dwarf horse chestnut) is in flower and will be followed by good autumn colour. It is a deciduous, suckering shrub from the South Eastern US.
Hydrangea Preziosa adds colour to the late summer. It flowers rose pink turning to reddish-purple with age, followed by autumn colour.