melanism

https://doi.org/10.1351/goldbook.14844
Increased black or nearly black pigmentation of skin, feathers, or hair of an organism, resulting from (increased) synthesis of melanin.
Source:
PAC, 2009, 81, 829. (Glossary of terms used in ecotoxicology (IUPAC Recommendations 2009)) on page 913 [Terms] [Paper]