What is the medical term for an abnormal condition of deposits of black pigment in different parts of the body?

Melanosis is the term for unusual black pigment deposits and it can be seen in the colon and rectum sometimes when a biopsy is done. This is called melanosis coli. This odd pigmentation is not cancerous.
Another condition is Black Lung Disease. It is caused by long exposure to coal dust and was (and is) still seen in miners. The miners used to work without any type of protection for the respiratory tract. It wasn't until 2016 that the final rules were put in place for the miner's protection.
Another dark pigment condition is seen in the skin and is called melisma.