The "color" black is not really a color. Black is the absence of light. Black objects have pigments that absorb all light and, therefore, none is reflected for us to be able to see.
Black holes are, by definition, non-luminous and non-reflective. It's pretty hard to see something that doesn't give off any light of its own and absorbs all incoming light. What we have seen are the...
It depends. If the scalp is showing, then yes. If the hair is bushy and thick then the only appearance of blood would be a liquidy, slimy appearance. If you need to test a piece of hair for blood,...
The first stellar object that was commonly agreed to be a black hole -- ie, no other explanation would fit the observations -- was Cygnus X-1, and this general conclusion was reached in 1973.