Liberty of London

I've been a MAC fangirl for a little over a year now.  My sister in law got me into it, and she's been a MAC rep for over 10 yrs (I forget the exact number).  I'm super excited about their next unveiling of Liberty of London, though in all honesty I get excited over every unveiling.  Lucky me, I get to go to one of the launch parties (squeal!)! 

So I have a question for you fancy British ladies, the age old question that never has the right answer -- what should I wear?!!  My first instinct is to buy something from Liberty of London itself, but the price tag says I can find something similar here in Portland.  We have a lot of boutique shops, and PLENTY of secondhand stores to piece something together.  What's trendy over there?    What says "I am fabulous!" What says I WANT TO BE BRITISH!