Lip serums are a great way to address the issue of dark lips. They can help lighten the lips and restore their natural color. Here are some of the best lip serums for dark lips:

1. Fresh Sugar Lip Serum Advanced Therapy: This serum is known for its age-defying formula. It contains Acmella flower extract, Kigelia Africana fruit extract, and sugar, which help to nourish and moisturize the lips, reducing the appearance of fine lines and dark spots.

2. Burt's Bees Overnight Intensive Lip Treatment: This product is rich in natural emollients, waxes, and oils, which help to lighten dark lips and keep them hydrated. It's a great option for those who prefer natural skincare products.

3. Clarins Instant Light Lip Comfort Oil: This lip serum not only provides instant comfort but also enhances the natural color of your lips. It contains plant extracts like hazelnut and organic jojoba oils that help to nourish and soften the lips.

4. Dermalogica Nightly Lip Treatment: This product is rich in Indian Gentian Extract, Sesame Seed Extract, and Shea Butter, which help to restore skin volume, hydrate, and reduce the appearance of fine lines associated with aging.

5. PCA Skin Hyaluronic Acid Lip Booster: This lip serum is formulated with ultra-filling spheres and hyaluronic acid that help to increase lip volume and reduce the appearance of lip lines.

Remember, the effectiveness of these products can vary depending on individual skin types and conditions. It's always best to patch test a new product before applying it all over your lips. Also, it's important to remember that sun exposure can darken the lips, so always apply a lip balm with SPF during the day.