Thank you all so much for commenting on the previous post! You've taught me things I didn't know, given me new insight, shared great stories and occasionally told me not to be silly... I'm grateful for all of it.
Although I should really answer all comments in turn, I will use this post to summerize and give some further explanation about the event.
First of all: the wedding itself. It starts in the afternoon and continues with a party in a small restaurant at the beach (all of those are rather casual locations). Secondly, the Dutch are notoriously casual dressers. Apperently, wedding guests in jeans are not uncommon here. Even though I don't consider that an excuse not to make an effort, it is something to keep in mind. Full evening attire would definately be considered 'over the top'.
And third, several of you suggested asking the bride about her idea on colours. I haven't yet but as I know this couple, they are usually casual dressers who wear a lot of black themselves (the groom to be is the drummer in the heavy metal band E plays in...). I know she will wear a formal ivory white wedding gown and he will wear a suit, but I can't imagine the two of them obsessing over the guests' choice of outfit.
All that being said, I did try to find other, non-black fabric yesterday. In colour(s) which wouldn't MISmatch E's outfit (which is still difficult. Some commenters suggested blue might work with his shirt. Well, lighter shades clash with the shirt, darker ones with the suit...). I did find two types of fabric in the same blue-ish, silver-y grey: thin polyesther satin (which I didn't buy because I really don't like that stuff) and cotton jersey.
I bought the jersey, with the thought that I could always dye it if the colour really doesn't work for me.
Oh, and I really like the idea of using an 'opposite' colour, I am still looking for such a thing (not so sure about orange though, I may have good experience wearing it, but just after the wedding, the European Football/Soccer Championship will start, and orange happens to be Holland's national colour at things like that...)
So, without further ado, these are my options so far (both still lacking hems and other finishing touches):
The black cotton voile dress. Here worn with my usual belt, a (too short) crinoline petticoat and my molded leather necklace. Not so much a bad look, but maybe a bit too goth for the occasion?
Here it is without petticoat and with that ribbon. As said, I'm not really a fan of the ribbon. It doesn't stay in place very well either.
And here is the jersey dress. The colour looks much better/less bad on me than expected. However you can tell I'm not used to dealing with plain, light coloured fabrics... I've made this skirt shape for knit dresses before but never seemed quite so in-your-face...
E says it's OK, I like the top but am not entirely sure about the bottom (of course, chopping it up and using it as a top could be an option).
What do you think, seeing the options 'in the flesh'?