Moral realism and moral anti-realism

What is the distinction between moral realism and moral anti-realism? How might a moral anti-realist nonetheless claim that there is such a thing as an objective morality?
What is a moral error-theory, of the kind defended by Mackie? Why is it a form of moral anti-realism? How does it differ from moral expressivism?
What is it about a Kantian ethics that ensures that morality is objective? Why is a Kantian ethics nonetheless a form of moral anti-realism? Why is such a proposal known as constructivism?
How does an Aristotelian virtue ethics, like a Kantian ethics, claim that there is an objective morality even while endorsing moral anti-realism? How might the analogy with colour be useful in this regard?
What is moral epistemology? What is the distinction between moral cognitivism and moral non-cognitivism?
Why is the moral expressivist and the moral knowledge skeptic committed to moral non-cognitivism? What is the crucial difference between the kinds of moral non-cognitivism endorsed by these two proposals?