Hydrangea ‘Blue Wave’ is also known as ‘Mariesii Perfecta’. It is a deciduous lacecap form and produces steely blue ( I know it always seems strange to say ‘steely blue’, but I think it means the colour of a piece of steel that has been overheated) flowers which are mauve to lilac-blue-pink when open in Summer.
As with most Hydrangea, the colour will ultimately depend on the pH of your soil, the more acid, the stronger the colouration.
Grow in moist but well drained soil of moderate fertility in a position that is sheltered from cold blustery wind….remember that hydrangea are naturally a woodland plant, and will thrive in a sheltered position with passing sun.
Hardy – These plants have had a hard prune, but are setting new growth point now.
The pic is of ‘Mariesii Lilacina’ which is similar, but has the serrated edge to the open flower more defined.