<unk>  is a form of hyperpigmentation associated with increased melanin.
It can also refer to:
Melanism
Ocular<unk> 
Smoker's<unk> 
Oral<unk> 
Riehl<unk>
Melanosis
Melasma
Blue nevus
Icthyosis
Ichthyosis
Scotoma
Erythrasma
Xerosis