Dinner party themes don't have to take their cues from food or drink: Color themes are a popular and fun way to make a meal unique. A Lemons and Limes party features yellow and green decor, and guests at Black and White dinners (which are increasingly popular) are often asked to wear only black or white.
Of course, it's easy to slip a little of the color theme into the food and drink -- lemonade, lime vodka cocktails, lemon bars and key lime pie are all easy items to add to your Lemons and Limes party. Similarly, a Black and White dinner can conclude with, say, vanilla ice cream accented with chocolate syrup, followed by White and Black Russian after-dinner drinks.
If you decide upon a more unusual color for your theme, like purple or yellow, don't dye your mashed potatoes or other foods; guests might find that a bit unpalatable.