Why’s skin colour such a massive thing?

It's a difference. It's the nature of man to find differences and the easier and more obvious, the better. From the moment three humans huddled together, alliances have and outsiders have been formed. When you get right down to it, we're a poorly adapted animal for this world - we are frightened and ill-equipped so we find our safety and defense in numbers.

Color doesn't dictate a man's character, but it is a difference because it suggests other experience and culture. Just as dangerous as those who use it to divide and oppress are those who ignore its existence altogether. We are different, we are varied. What we'd do well learning is that "different" doesn't mean "bad."