Coal
moss, teal, aqua, lime
Spiv
orca
rook
bird
Some choices: drape, blind, shade
The word "shade" implies darkening. So, yeah, it probably is.
the 5 letter word for colour slightly is shade
A four letter word starting with the letter a is able.
avocado, emerald
There is no silent letter in the word "black" c is silent in the word black
It depends on what you mean by 'four letter word'. Thea has four letters, so yes it is. It is not a swear word, so it's not that kind of 'four letter word'.