here is my experience

I was at one once. To my surprise, the atmosphere was way lighter than i anticipated. Some people even dressed in some bright colors. 

My advice would be definitely going for the safe side. Wear black with some decor (belt/jelwery) in a different color. Light smile is good. Do not talk too much. Be prepared when people ask you how do you know the person who passed awa--that's usually the ice breaker in an occasion like this.  

Hope this helps