I am about to lean toward a concentration on morality and away from ethics but for the sake of continuing a great conversation. Id say that as the quote from your post stated, black and white is easy, grey is hard, but to paraphrase CS Lewis, that people make mistakes when trying to reach the objective right, doesnt mean there isnt one, just as we can mistakes when calculating sums in math but yet there is still a correct answer to strive for.

One more great quote:
...as you find a few people who are colour-blind or have no ear for a tune. But taking the race as a whole, they thought that the human idea of decent behaviour was obvious to every one. And I believe they were right. If they were not, then all the things we said about the war were nonsense. What was the sense in saying the enemy were in the wrong unless Right is a real thing which the Nazis at bottom knew as well as we did and ought to have practised? If they had had no notion of what we mean by right, then, though we might still have had to fight them, we could no more have blamed them for that than for the colour of their hair.
I know that some people say the idea of a Law of Nature or decent behaviour known to all men is unsound, because different civilisations and different ages have had quite different moralities.
But this is not true. There have been differences between their moralities, but these have never amounted to anything like a total difference. If anyone will take the trouble to compare the moral teaching of, say, the ancient Egyptians, Babylonians, Hindus, Chinese, Greeks and Romans, what will really strike him will be how very like they are to each other and to our own. Some of the evidence for this I have put together in the appendix of another book called The Abolition of Man; but for our present purpose I need only ask the reader to think what a totally different morality would mean. Think of a country where people were admired for running away in battle, or where a man felt proud of double-crossing all the people who had been kindest to him. You might just as well try to imagine a country where two and two made five.

-CS Lewis, Mere Christianity