The whole idea of colour was entirely different in Ancient Greece, Homer for instance write that the sky was a Bronze colour and that sheep were the colour of wine.

The Greeks when they went to war, didn't fight under a flag. That notion didn't arise until the Romans who were excellent vexologists.
Although it has been suggested that Alexander the Great may have used Blue and White to mark his troops, the idea is unfounded in actual archaeology and appears to be a modern reconstruction of history post 1821.