What colour is the sky? The ocean?

You might think the answer is obvious: they're blue. Maybe not, though. Homer's seas were 'wine-dark', and he never referred to the colour blue. He wasn't unusual in this; most ancient texts don't use the word. Exactly why this might be is a matter of some debate, but one explanation is that in ancient societies, blue was an unusual colour. Blue dyes came later; blue flowers are the result of selective breeding; blue animals are hardly common. Which leaves the sky and the sea, and maybe they're better described as white, or grey, or wine-dark. So maybe people didn't say 'blue' back in the day, because the colour was so rare that it needed no label.