When it comes to attending weddings, there are a few rules to keep in mind with your cocktail dresses.
If your dress is white, forget it. Only the bride gets to wear white. This is her day and no one gets to take that color except her. Black cocktail dresses are also out at weddings. Black is a bit somber of a color for a wedding.
Pink Cocktail Dress
Cocktail Dresses For The Occasion
Now that you know what colors NOT to wear, you can focus on what you can wear. If the wedding is semi-formal or an informal evening event, a regular cocktail dress will do just fine. If it's a formal evening event, you can still wear a cocktail dress, but it needs to be very dressy (think beaded or heavily accented with a wrap and stunning jewelry.
Women I pick a Cocktail Dress for you on Valentine here you go