Colour lacking in the garden July, August.

The garden is at it's most colourful now with iris's and roses looking good. Thinking ahead, I find July and August there is a lack of flowering plants. I find the choice of plants (especially perennials) here quite limited and have supplemented with bits dug up from friends and family's gardens in the uk. Can anyone recommend anything flowering or even interesting foliage that will (if cared for) give colour and interest in the, hopefully, hot summer months. Many thanks.