You have a linear epidermal nevus. I'd advise either surgical excision and suturing of the lesion, possibly in stages, or shave excision, and electrosurgery of the base. Best to chat with your dermatologist about the best option for you.
If you are having non-ablative procedure done, where you skin is not being peeled or physically damaged, then you should be able to wear make up right afterwards. If you are having ablative procedure, like laser peel, fractionated laser, then you will not be able to wear makeup for few days...
Dark pigmentation on the skin can be due to melasma, age spots, and sun damage. Melasma is a specific hormonally-influenced skin condition in which pigmentation is deposited by overactive pigment cells in your skin.
In our office, we individualize treatments for melasma and skin...