A long shower bouquet of vivid purple orchids would be absolutely fabulous for a formal wedding. The orchids are so breathtaking that it would be best to create the bouquet using only that variety of flower to let them shine in all their glory.
One lovely idea is to add some tiny blueish-purple flowers (also called grape hyacinth) to a mixed bouquet of lilac tulips, mini irises, and lilac spray roses.
The compounding of sizes, shades, and textures will make for a very interesting bouquet.
Pale lavender garden roses combined with white peonies and lavender colored lisianthus would make a magnificent bouquet for a spring garden wedding. A beautiful variation on this would be to substitute sweet peas in several shades of purple for the white peonies.