You can't go wrong wearing red or green to a Christmas party, but avoid a plain red sweater or dress. Here are three ways to wear the colors of the season in a more sophisticated manner.
1) Choose your palette. Use pattern and texture to add a bit of interest. A green checked shirt plus a green striped tie plus an olive suede vest looks festive and chic. Adding black and some fur to a red dress looks bright and stylish.
2) Make it shiny. Look at the red plaid pants, green skirt or red patent pumps above; they all work because they shine.
3) When in doubt, accessorize. If head-to-toe red or green doesn't feel quite "you," then choose one accessory in a merry color. A black silk T-shirt and simple black pants plus red shoes or green earrings will make a subtle but effective statement. A red pocket square will pop on a black blazer.