There are some beautiful deep blue delphiniums and also iris.

there is a darkish nigella and a cornflower. also look for annual larkspur [looks like a delphinium]
depends on the time of year too. spring - muscari also.

There's a dark blue flower florists use a lot called Lisianthus - comes in other colours, but the blue one is the colour of Bristol glass, not sure if they'll be available at the right time.

Thanks ladies, I have sent your suggestions to her, personally I would have them all, mixed, but its not my wedding!! Its in April if thats anymore help.

I grew some lisianthus from plug plants......not easy but they did flower the most beautiful were the white with the blue edges...

Out of curiosity I googled royal blue flowers and got the above delphiniums and iris, also deep blue hydrangea and grape hyacinth....difficult at the time of year but one bouquet took my eye and that was white roses with deep blue feathers....I thought it was stunning better than any of the dyed flowers or silk ones I thought but its really what she has in her minds eye.....

Marion, Blue would look nice mixed with whites, purples, pinks and lavendar colours, as blue tends to deepen an arrangement adding another colour would lift it. Or maybe use delphinium, pale blue hydrangea, blue thistle, blue statice, blue veronica & iris, for my daughters wedding we used the material that was cut from the length of her dress to wrap around the stems of her bouquet with pearl pins, it looked lovely.

April probably rules out delphinium and even iris would need to be the early ones...

Lisianthus was what sprang to mind for me...and yes, those early Iris that florists use as well MG. I love the idea of using some of the bridesmaids' dress fabric too...that would really be lovely if they are the blue colour. Back in March, my OH gave me flowers...http://www.growsonyou.com/karensusan63/blog/18923-birthday-flowers-on-a-jubilee-theme

as you can see..they have royal blue Agapanthus in there, so they must be available too! They would be great!

My first thought was lisianthus too. Have a word with your florist because they can often order things if you give them enough notice. There are plain blue and purple but also some where each bell is blue and white, which lifts the arrangement as Grandmage was suggesting.

Thank you so much for your suggestions, they are all beautiful, I have sent her a list and suggested a mixture and she was thrilled that you all helped her.

A Pleasure Marion, it was interesting to see the ideas

As a florist (with too many years experience!!) All of the above suggestions are wonderful, what a reply! just a thought though... the natural light is not that great in April, too many dark colors next to a white or ivory dress do not photograph very well, however there is a deep blue anemone called "Jerusalem Blue" which is available or 'campanula", also in blue.Delphiniums are available in april if you order them from your florist and Eustoma ( lisianthus) is available all year round . Steragram is right, the white and blue edged one is very pretty and its called "vulcan purple picotee. Lynda

Perhaps you could let us know what she finally decides on!

Thanks so much for all of your help, I will certainly let you know what she chooses and hopefully post some pictures, at the moment she is researching them all and getting really excited, when I suggested the idea of mixing them she thought it was a great idea and I personally think it will be so much nicer, and softer than just say sticking to one or two different types of flowers.