What do you call that disease which makes your nail became black?

Well you can get nail discolouration due to alot of different activites. Normally it is common that after an injury your nail turns black. It will usually fall off and inturn you will grow another.

Worse case is Melanoma, this is rare, but has happened.

Here is an article on the subject: Please click on the link below Healthy Nails

I Hope i have answered your questions.