This is the most common for of endogenous pigmentation.
Most people have some melanin and some have more.
Compare the two patients above to see the various clinical colors of melanin. All of the other choices may be associated with an increase or change in melanin pigmentation. Although smoking may cause a pigmentation on the gingivae, this patient's is normal physiologic melanin. On the second patient above, also note the dark line at the cervix of crown restorations, representing the metal at the margins of porcelain to metallic crowns. Also, on this patient note the prominent leukoedema of the buccal mucosae.