A blue bridal bouquet might consist of blue and white flowers, blue and lavender flowers, blue and yellow flowers, or simply blue flowers.
With blue being the color of the sky and water, it's a natural choice if you are considering a beach wedding. Martha's Vineyard is a hot spot for destination beach weddings. Here are some resources if you are planning a Martha's Vineyard beach wedding
There are a few commonly used blue flowers: hydrangea, elphiniums, cornflowers and Hyacinths. Roses are also used in blue bouquets but they are generally grown as purple roses and then died to a blue shade.
Here are some ideas and photos of blue wedding bouquets: