Ehm, ... what the Hell? Look up the etymology of black sheep. Do you know what the following means: The black sheep of the family - well...do you?
Does that mean that we're not allowed to use colours in a symbolic form any more...? Does that mean that I'm not allowed to use the word yellow, black, red, white, coffee..wait..what is the problem again?
http://www.phrases.org.uk/meanings/66250.html
The colour black, in symbolism, always had a bad meaning in Europe.. like..black cat, black crow, etc.
it is like the saying 'red headed stepchild'.
afa the other part. they associate black with night time and that is primarily when bad things happen. especially if you are superstitious.