Don't know whether ahy of these would help: pineapple mint has light green leaves variegated with cream. Beetroot has purplish leaves, and carrots have feathery tops, but they would probably droop as they wilt very readily. Dill and fennel would be better, or asparagus fern. Golden marjoram has pretty lilac flowers. There is a red cauliflower called Graffiti but caulis are tricky to grow. There are lettuces - look up Sierra, Lollo Rossa and Navara, and a curly kale called Scarlet. You might look at rhubarb chard (Charlotte), and also Cardoon(harvest Autumn so it might not be ready in time)
SAll these can be found in most seed catalogues, but they are certainly all in www.dtbrownseeds.co.uk

Might be worth contacting them and asking about harvesting times where you live.

Ooooh, very keen on the idea of beetroot and lettuces - what a great idea. Golden marjoram also sounds lovely. Can't believe I haven't thought to look in seed catalogues! Will get one delivered ASAP.

Thanks for the pointers.

How about eryngium - lovely silver spikey blues? Also called sea holly plant. Excellent long lasting cut flower. Buy at any nursery in spring for flowers in summer and autumn. If you grow by seed they won't flower until the following year. Agapanthus blue is another long lasting cut flower with striking flower shape, that flowers late summer to autumn. If you have a friendly local nursery, give them a list of plants and numbers of each you would like, they can often store them for you, deliver to the wedding and all your helpers/florists have to do is cut them down and display their flower heads. The plants, being perrenial, can then still be planted out in your garden to remind you of your day in the years to come!

Lovely ideas Avgk, but Lilmisreading was looking for herbs and veg.

No worries! Figured I would need to grow flowers as well in case things don't work out and as back up.

We'll head to a nursery this weekend to see what help they can offer.