Hot wedding guest wear

[Glitteryfrog]

I'm attending a wedding in Spain.
Two questions:

1. how dressy is a Spanish wedding. It's civil not church and in the evening.
2. what on earth do you wear to a wedding in 40oC heat

Has anyone seen anything suitable?
I'm a size 10ish, 5'8 pale with red hair, athletic shape - good arms and legs.

www.apricotonline.co.uk/mall/productpage.cfm/womensclothing/_5051839175037/461694/Navy-&-Pink-Painterly-Dandelion-Print-Midi-Dress

I wore this to a wedding yesterday and I was lovely and cool - it looks ok with heels or flats which is good too