Dire need of help...

So I am throwing out the question to y'all and need as much help as possible:

What would you wear to a evening (semi formal) weddding reception? The Dress I wanted to get is no long available... :( aka I took too long to buy it and went shopping today but ended up walking with dresses for other engagments. :|

Background a bit, the bride is one of my best friends and though I'm not in the wedding I have about 10 million jobs a BM would have (long story...but pretty much it was have no one in the wedding or have 25 bridesmaids... she choose no one). Her colors are silver and white (obviously I can't go in that color scheme). Can I wear patterns? What types of fabrics should I lean towards?

HELP!!