While a reception may feature fine food, alcohol, socializing, music and possibly even dancing, any event related to business and involving one's coworkers and supervisors must be treated with a great deal of consideration. Regardless of all the other elements at a business reception, think of it as a very large dinner meeting, even if business is never discussed. The key is to dress professionally, giving, if possible, your ensemble a slightly more evening look.
While the protocol for men is infinitely easier, some changes should be made as well. The simple answer for men is to wear a dark suit with a dress shirt, a silk tie and dress shoes. However, you want to make some distinction between your ensemble for a regular day at the office and a business reception. Consider wearing a French-cuff shirt with cufflinks. If you have a pocket square that matches one of the colors in your tie, display it in the breast pocket of your suit jacket. Accessorize by wearing any watches or watch chains you might own.
Women are both luckier and less fortunate than men: they have more choices and options for attire, which can make the answer seem more nebulous. Don't fall into the common trap of wearing a dress that shows too much skin or donning open-toed shoes. Dresses are permissible, but they should be a dresses that would be an instant pick for a business meeting, not for a wedding reception. The hem of the dress should fall below the knee. No cleavage should be seen and the shoulders and back must be covered.
For a business reception, the safest option is a skirted suit with stockings and closed-toed high-heeled shoes. However, like the men, you want to make a clear distinction between the garb that you wear everyday at the office, and the ensemble chosen for this event. Consider choosing a frillier blouse underneath your suit jacket, one that might have a tasteful ruffle or bit of lace here or there--nothing flamboyant. Your shoes can be a marvelous way to express distinction--consider wearing shoes with a slight adornment, such as a leather flower, silver buckle, understated chain or button. Feel free to accessorize but do so tastefully. A jeweled necklace with beads that match your suit is a lovely choice, and a watch with a beaded or linked band is also an elegant option. Earrings are fine, but to be on the safe side, don't wear anything that dangles past the lobe. Pearls and diamonds are often best.