Selecting makeup colors can be difficult, especially if you are trying to coordinate with an outfit. One can match the lipstick to the ensemble, but there are other approaches to best complement your beautiful purple dress and accessories.
View your dress in natural light, and in light similar to the light available where you will be wearing the dress. Is the purple more reddish, or bluer? This will help you choose accessories and makeup.
Now take a look at yourself. Note your hair, eye, and skin colors. Are there predominantly warmer or cooler colors? If you're a green-eyed redhead, you'll need very different colors than a raven-haired woman. Some shades of deep purple look equally good with silver or gold, which can be useful for selecting makeup and accessory colors.
You could try to match the dress with a lipstick color, but this can be tricky if you don't have strong coloring. Neutral colors and tints work well for most skin tones. Golds and a sheer, warm plum color flatter warm skin tones, while sheer, cool purples and berries work well for cool complexions. Beiges work well on both.
Try it on! Play with shades at the cosmetics counter. Bring a swatch of the dress if you can. Remember, the lipstick needs to look good on you, not just match the dress.