Why are some people gums brown?

Pigment content . Skin and mucosy membraines like gums color depend on number of pigment cells containing melanin. Large amount of melanin makes skin and mucosy membranes darker.
Pigment. People can have different amounts of pigment in their mucous membranes that can look like brown spots on their gums.
Pigmentation. Dark gums are mostly seen in dark skinned people. The gum discoloration may be present in patches. The extent of gum discoloration and the intensity is different for different individuals. Dark pigmented gums don’t mean that they are unhealthy and are not an indication of a disease.