adjective

1. Having an absolute or (more often) relative lack of light.

   “The room was too dark for reading.”

2. (of colour) Dull or deeper in hue; not bright or light.

   “my sister's hair is darker than mine;  her skin grew dark with a suntan”

3. Hidden, secret, obscure.

Synonyms: hopeless, negative, pessimistic, unenlightened, deep, dim, gloomy, hidden